I think I’m pregnant but..........

So I’ve always had complications with taking pregnancy test. I have been pregnant 3 times and not one time has a test came back positive. I was losing my first one as soon as I found out I was pregnant. My second one I took pregnancy test after pregnancy test followed by more pregnancy test and all were negative. Long story short I went to the er due to the bad migraines I was having and they tell me im almost 6 months pregnant. I can’t even explain how I felt I was worried about my baby because I smoked cigarettes at the time but also I was confused I had a regular flow every month nothing was different I didn’t feel the baby I didn’t gain weight my baby came out healthy thankfully my third pregnancy was similar my test was negative then changed to positive so they took my blood said I was pregnant but my levels were too low to be pregnant so they took blood again. I bled with this one too just not my whole pregnancy. Ok so two weeks ago or so I noticed I was really nauseous about everyday so I took a test negative so I pretty much blew it off but lately I been nauseous still and I keep feeling a flutter or something in my stomach can’t lay on my stomach I also noticed I’ve been going to the restroom a lot I went to the doctors explained everything to them they took a test negative blood work negative I just don’t know what to do they won’t give me an ultra sound I don’t want to find out I’m pregnant late in again