Right side back pain!

I’m 20 weeks and having sever back pain in my back right side. I try stretching and bending over but it doesn’t help! What could this be, I’m a first time mommy and have sooo many worries. Am I also to small for 20 weeks? I feel like the back pain is being caused because the baby is against my back somewhere which is making me smaller. I just don’t know, stressed to the max!!