Had A Regular Periods. Now Have Little Variation. Pregnancy Test Shows Negative. Have Abdominal Pain. Suggestions?

I have a lil problem that I would like to share wit u. I always av regular periods but since 2 months ago evrything changed. I was supposed 2 see ma period on the 28th of May as usual but instead it came on the 1st june n nw I dnt no how to calculate n no wen nxt to see my period n I av nt seen ma period 4 d month of june, I was expectin it 2 come like on the first of july lyk it did 4 d month of May n I didn't take any pills. I was curious n did a pregnancy test twice buh both turned negative. I dnt no wat else to do bcos am used to my regular periods n now av lost count. One more thing most tyms I av dz lower right abdominal pain. Plz Ma I nid u 2 explain to me wat it all means.