Confused

So I was 7 days late and tested. I got a very very light positive. I then started bleeding very dark for 2 days with heavy cramps. Everything stopped for a day and I started spotting lightly for another 2 days.. not my usual period, it felt strange.. I took another test and that had another light positive. I then went to get blood work done the next day. It came back negative.. I have had like all the symptoms of pregnancy! I’m so confused to why I would get positive urine tests but a negative blood test. I’m going for an ultrasound next week but I’m so frustrated. I have been trying for 3 years with my partner. Anyone have any suggestions for what might be going on? Also my mom with her first pregnancy had twins but got all sorts of negative tests until she got an ultrasound at 5 months.