IS THIS NORMAL???? help

hi all not sure if im in the right section but was wondering if anyone could help me or if any prof knows of this....

My last two pregnancies since about 8 weeks i could feel,when i lay flat on my back,my uterus clear as day like a big lump starting above my pubic bone...the whole thing would just be sitting there, sticking out....sounds weird i know,well those two pregnancys ended in a 35 weeker and a 30 weeker baby not to mention a large tummy and spd and sciatic nerve problems from about 18 or so weeks.....and measurment 6-8cm above the normal weekly measurments

now to current, i am 10 weeks pregnant and although not as bad as the last 2 pregnancys i am having the same thing happen again so :

1) am worried i will have another premmie baby and

2) am wondering wth is causing this.....

my 6 week u/s was fine apart from beany being really close to the placenta which made measuring hard everything was fine ...and with the others no mention of odd shaped uterus...anything extra being around it etc....

Also noone has even been able to tell me the cause

So was just wondering if any other BB girls have had this or if there any profetional ppl that know of this etc...i am really worried that this will cause another premmie as they had no idea why they happened and my first pregnancy didnt have this and was a 39 weeker