I've been seriously questioning my gender for over a week now

I've been aware of my wish to be the opposite gender ever since I seriously questioned my gender two years ago. I then decided I was just a weird cis person who really wished to be the opposite gender. I left it at that and even felt embarrassed for questioning in the first place while still being conscious of the fact that I had this constant longing to be the opposite gender. Anyway, it resurfaced again and at first it felt really nice. Like I was constantly fantasizing about living life as the opposite gender and I didn't want it to end. But then doubt crept in and I've been going back and forth between intense doubt and brief clarity for about a week. Like it's all consuming. I'm always thinking about it. I spend literally like from the moment I wake until I fall asleep thinking about it. Somebody please help me.