What Causes A Heavy Menstrual Flow,sore Breasts And Nausea?

Hi i am 40 years old and had a sterilization surgery 6 years ago right after my son birth. Last month I got my period but realy strange as I am a very heavy flow which lasts up 6 or 7 days. But this time it came very light just spotting on the first day second day a light flow but nothing to fill up a pad and the rest 3 days just spotting. I have taken a urine test like 2and half weeks after I had intercourse but it came out negative. Then I took several home pregnancy test a week after still negative now I'm like 5 weeks I took another test but it look so light could not tell and the second one came out negative. My breast is heavy and realy hurts when I take off my bra. I feel nauseous and have hardly any appetite. I lost 3 kgs but my pants is tight around the waist and I have a small tummy. This so confusing to me....and I'm tired all the time. In the beginning of May I took a general blood test and it came back good nothing negative. I don't understand why I still feel like this and a few days I started getting needle sharp pains in my womb. Could I still be pregnant even though all those test came back negative. The only time I had unprotected sex was on May 16.......I'm truly confused and upset ....