There's so many things that this could be,
Having a child can be a strain on the back alone as it is, and it;s always safe to visit your Dr to have a physical done to see if he/she would want to take it furher.
If these are the only symptoms you're experiencing then I honestly woulnd;t worry too much. Have you ever had a good old back rub? Or a really hot bubbly bath to relax your muscles?
Make sure you're sleeping on a good surface as well, all of these things can add up to back pain.
I;m not a Dr by the way, just offering a little persoanl advice since I sit at a computer desk all day and get back aches too :)
let me know if you see a Dr or if things get better through relaxation methods!
is is your sciatic nerve?
If so, chiropractic assistance and physiotherapy can help with that.
I hope that you find out soon, living in pain is not fun.
xx