You should really try prenatal yoga! I'm 30 weeks and if I don't, I have similar aches. Especially my pelvis/hips; I almost can't walk when i get up in the morning. But if you can make the effort, the yoga makes it ten times better for me. It will help with the back pain too. As far as headaches, it's normal, I do notice I get them much less with the yoga. Might just be me, but hey it works! Talk to your Dr if it gets worse, see if he has suggestions.
I'm almost 31 weeks. I have back pain and occasionally when im walking my leg muscles go super tight which makes it painful. I have lower abdomen pain too sometimes. But I cant say y pelvic feels like it's on fire