Constantly convincing myself of things I know are untrue, i'm not sure how to stop.

Hi everyone. I used to be a subscriber here a year or two ago but then my life made a turn for the better and I was doing alright up until this past week. I don't have officially diagnosed depression, but when I go back to school in 2 weeks I intend to seek counseling there and see what a professional thinks of my mental state. Within the past week, i've started convincing myself of things that are untrue revolving around my girlfriend and my relationship. I was unsure where else to post, I figured if anyone would've had a similar situation it would be someone here. If not, please direct me to a better subreddit to post this in. I couldn't think of one.

I love my girlfriend and I am confident that she feels the same. We have a healthy relationship, but we hit a few bumps this past weekend and the one before. We worked these issues out and we're back to normal. I'm not just assuming we're back to normal, we had a fun weekend and had fun together. There is no question that there is nothing wrong between us. However, I keep convincing myself there is. I keep convincing myself she doesn't love me or care about me, and that she no longer wants to be with me. She's made it clear that she does (through her words and actions) and so do I. I keep convincing myself otherwise though.

A situational example would be this past Friday. We live 3.5 hours apart, we met at school. In 2 weeks well be 1 hour apart but that's besides the point. I came out Thursday night and I hung out with her family Friday while she was at work. She was supposed to be home at 5 but she ended up having to stay until 8:30. I immediately concluded that she was picking work over me, and that she didn't want to see me. I talked to her when she came home and made a big deal out of it, about her picking work over me. She was hurt and confused. By Saturday I realized she hadn't picked work over me, it was just an unfortunate event out of her control. I had thought WAY too far into it, and I had turned a mole hill into a mountain in my head. There are a few other examples very similar to this.

Basically, the majority of the problems I think we've been having lately are ones I've created in my head through worrying, overthinking, and reading too far into things, when in reality we haven't really had any major problems at all. I wrote these thoughts and others on paper and read them to her, about it being all in my head. She saw it was that way long before I had even realized. She agrees that I should seek help.

I don't work with school coming up, and she does. She graduated and works a 6:30-5, 6, sometimes as late as 9, 6 days a week. Therefore we don't talk during the day, and I don't really do much at home. I stay busy the best I can but there really isn't much to be done during the day. It leaves me with plenty of time to overthink and worry about absolutely nothing. The other day she yelled at me because I had sent her probably 15 multiple page text messages about how bad I needed her, how I thought she didn't love me, and how I thought she was going to leave me even though she explicitly said she isn't going anywhere and wants to be with me. She managed to calm me down and convince me otherwise, and everything went back to normal. I was so confused as to why I had been worried about all those things, it's obvious that none of them were legitimate concerns. The next day I had the same worries and tears all day, tearing away at me and breaking my heart. I didn't text her though, and when we talked at the end of the day, everything was fine. Once again, I was so baffled as to why I worried myself sick for absolutely no reason once again. Unfortunately, it's the same way today.

I'm looking for a way to cope. I'm looking for a way to destroy these doubts about nothing, because it's driving us apart, and its my fault. I'm looking for a way to reassure myself that everything is okay the way I know it actually is. I want to know what's going on in my head so I can fix it, I don't want to put this burden on her any longer.

Thank you all for your help.

EDIT: I was just at a physical and I saw a poster about depression, it listed some symptoms like lack of interest in things, trouble sleeping, and loss of appetite/trouble eating. These are all problems that started last weekend when we actually did have an argument over something that did lead me to feel pretty down, I haven't been able to shake the feeling since. Perhaps I do have depression?

DOUBLE EDIT: I just read online "Temporary emotional responses to the challenges of everyday life do not constitute depression". Fair statement, but it makes me wonder if this is something that's going to pass or what.