Pregnancy tests- negative! what to do?

* COULD BE AROUND 18-19 WEEKS* 

*STILL GETTING PERIODS EACH MONTH* 

Is it safe to say I'm not pregnant? Iv had pinging pains around my stomach , constipated on and off, reoccurring UTIs, aching lower back, pains through my boobs but don't her to push on-towards when I'm due for my period they start to hurt and then I get my period and the pain goes away. My periods have actually been early, not late. But I only get bleeding when I'm on my placebo week pills. I have 3 days of light spotting when I wipe and then heavy to about medium flow bleeding for 2 days and a couple of days of just medium bleeding. 

I'm 23 and married but just so clueless as to what is happening! I went to my GP and she did a PREGNANCY TEST it came back negative.