Negative hpt but stomach growing and feel pregnant

Patient: Ok, here goes. Back in Oct of last year I had a positive hpt, but about six weeks later I had a miscarriage, or so I assumed, getting my menstrual cycle. Then i didn’t get a cycle again after that for about 2 months. Now it gets strange, my last possible cycle was the end of January. But, it was different, it was dark blood, and only came in a few small intervals, and there was not much of it. Now, here I am two months later with no cycle, my stomach has grown (to about the size i was with my ten year old twins)…which in a normal pregnancy is about the size of 3 to 4 months on a woman. My breasts are very tender and i absolutely feel pregnant, BUT i have taken 4 hpt and they all came back negative?? I am on some medications for an injury to my back, so i don’t know if thaat would interfere with the results? Plus my stomach is hard and round standing up, but softer laying down….i don’t know what to think??? can you help me please.