pregnancy bleeding or early period?

Fiancé and I are not trying for a baby (yet; we're planning on it after our wedding reception in October) but we are in stable enough financial and life space where having a kid would not be a disaster, so I've been a bit more careless than usual with my oral contraceptives. My period has been suuuuper regular for YEARS (except for a random missed one in November).

Then last week, week 2 of my cycle (just before ovulation), I accidentally missed four days (Tues-Fri) of the pill. On Friday, I got the shivers and a lot of anxiety, and I started bleeding. Took 2 pregnancy tests immediately - both negative. The bleeding lasted until yesterday (Monday) evening, about 3 days, moderately heavy with mild cramping and a lot of anxiety (typical of my periods, albeit a day shorter). It was gone for a while but I'm now spotting lightly. I have been feeling nauseous on and off all day.

I scheduled an appointment with an OBGYN, but they can't get me in till late September. I'm holding off on calling my GP about this for now (we need to save funds for our honeymoon and for future medical expenses).

I am not under extra stress, have maintained a consistent exercise routine and diet, and am not taking any new medication. I am 32 and sexually active but very careful. The pill has worked great for my partner and I for many years. I've never been pregnant before and have no idea (aside from research online) what the early days look like.

Is there a chance I'm pregnant or is this possibly something more serious? I would rather the first, but don't want to call the doc unless I get a positive test.