I have irregular periods, sometimes 3 months apart or twice in one month

HELP..... I have irregular periods, sometimes 3 months apart or twice in one month. It comes when whenever it wants to I guess. In the beginning of January I had sex with my boyfriend on the first and second. We never use a condom and I'm not taking anything. However after we had sex I had my period on the third the next day. After my period, every week we have sex and about 2 or 3 weeks later my breast were sore, I started to get cramps, frequent peeing and consipation(which is never a problem). I took 2 pregnancy test both negative. On febuary 24 my cramps got worse my boobs were really sore and the next day my period came and its heavy. Its now Feb 27 and I still have the same symptoms. Last night I woke up to my cramps. Could I be pregnant still?? Please help