I just turned 31wks yesterday, Is it twins HHHEEELLLPPP

Hi ladies!I was just wondering if you all think it looks like I'm having twins or not. I know you can't just look at someone's belly and tell if they are having twins or not, but it doesn't hurt to ask. Just to give you some history of why I think I'm having twins: I didn't find out I was pregnant til I was 6wks via the emergency room. I went to the ER due to shortness of breath and pain in my lft wrist. I thought it was due to aniexty from starting a new job, but left knowing it was due to pregnancy. This will be my children's father & I third child. We have a 2yr old daughter & our son just turned 1yr old 9/21 (so as you see we weren't planning on having anymore children, at least not this soon). I use to be a twin, but my twin didn't survive, if it would've lived we would've been the 1st set of twins in my family. 2wks after my 1st ER visit I had to go back due to not feeling well again & they gave me a ultrasound. The nurse kept kept saying " it looks like you might be having twins, but we only see 1 so far." All I know is this pregnancy has been way different then my other two pregnancies. I've been more tired and just this strange feeling (I can't really describe it). Before I even knew I was pregnant I used to wake up so nausiated that I could barely get up to take care of my two young children, but it didn't dawn on me at the time that I could be pregnant,because I didn't experience morning sickness with their pregnancies(at least no where near to that extent). When I went to my last doctor appointment I gained 15lbs in 2wks & it all went to my belly. I told the midwife I don't know how that happened, because my eating habits haven't changed (So confusing). I'll see when I go to my next doc appt. next week. I also wanted to add that when my baby move it feels she's in two different areas of my stomach at the same time!?!? I'm going to tell my midwife my concerns when I go to my next appt.