What Causes Constant Pain In Lower Back During 39 Weeks Of Pregnancy?

Hi, I will be 39 weeks pregnant tomorrow and I have been really constipated for about 4 days now! I am really uncomfortable and have this constant lower back ache that feels like someone is hitting my spine with a hammer that random gets worse and radiates to the front! I feel like I have to use the bathroom and when I try it just hurts everywhere in my lower back and lower belly which there is a lot of pressure aswell! I was told that laxatives could make the baby go inside of me which isnt good and my doctor told me to eat lots of fruits and vegetables and drink a lot of water which I have already been doing and nothing has helped! Is there anything else I can do to help?