Pregnant or sick? What's wrong? 3 negative HPT's, nausea for 2 days, heavy clotty period.?

Help! My period came the 13th of April. I had unprotected sex the 18th and 25th of April. My periods have always been irregular, but I decided that I would used the App "MyDays". Well the app told me that my next period was supposed to be the 13th of May, my ex boyfriend started to worry me, but three days after (May16th) I got my period, it was heavy, clotty and long, it also smelled really strong by the end of it. Immediately after my period ended (May 21st) I experienced pelvic pain, abdominal pain, slight back pain, and nausea that lasted for two days prior to taking a hpt. I took two hpt, one in the afternoon, and then the other one I took the next day right after I woke up... they both came up negative, I also took a test a week after in the clinic, that also came up negative. But the pelvic/abdominal pain is still here! I am also constipated for about three days then have diarrhea for one day, I had a little bit of blood in my stool just once, my stool has mucus on it, my pain began in my lower left side, then travelled to my whole stomach (horrible pain) then to my right side, and both sides of my abdomen, and now it randomly appears on any side of my abdomen/pelvis, the pains are dull/achy and sometimes sharp, they get worse during the night, and range in severity but are always present. I have been in pain for a little over 20 days now, I just want to know if I am pregnant or not? sorry for the long post :/