Negative tests, but feel pregnant?

I had unprotected sex on September 15th. I took plan b the day after and started my period 2 days after I took the pill. I had a full period that lasted 6 days. (It wasn’t light). I was still a little nervous that I could still be pregnant and I took 2 tests 1 month later. Now that it’s December, I’ve had 3 periods since I’ve had sex. I last took a test about 2-3 weeks ago and it was negative. I know it’s not common to be pregnant and still have a full period, but lately I’ve been feeling bubbling in my stomach and it’s been hurting me. Also lower back pain. Hard to explain, but I feel very bloated. I feel it, but I don’t look it. If that makes sense. No other symptoms. I’ve been checking my stomach everyday in the mirror and haven’t seen any growth. If I “were” to be prego, I’d be about 15 weeks, since my ‘last’ period before I had sex.

Since it’s been about 3 months, is it safe to say I’m not pregnant if the tests are still coming out negative? And I’ve had 3 periods? I know it sounds so stupid to ask, but still wondering if there’s a possibility.