I'm 20 weeks and 3 days and have been experiencing bad back pain and stomach cramps that come and…

I'm 20 weeks and 3 days and have been experiencing bad back pain and stomach cramps that come and go. It hurts more then usual cramps when I could tell it was just the baby growing. At my last ultrasound they told me she was toward my back and that she could sit on a nerve but they said she could move. That was about a week ago. It felt like what they described Braxton hick contractions to be but when i read about them it said they don't happen so early. So I wanted to see if anyone else had felt this and found out what it could be and if I should be worried? I'm FTM so I worry about a lot but I really don't want to keep running back and forth from the ER.