Hello Dr My Son Of Sixteen Has Been Complaining About

Hello Dr my son of sixteen has been complaining about a dull ache in his lower left side of his back, which at times he can feel the pain in the same side in the front. He has no problem urinating, he seems to be walking just fine, he is slightly built having been a dysmature/premature baby at 600grams but otherwise he appears to be in reasonable health, the pain has been there for about a week now, he likes to do all these dance movement lol and he sits a lot in front of a ps4 playing on line games, a few weeks ago he had a very bad neck pain but that has cleared since then, he has no fever, his not vomiting, at times especially at night he says his tummy sounds like it is grumbling, he has no problem going to the loo, he also says he feels like he has hunger pains, but his well but not over weight at all, I truly do not know the answer perhaps you could help I realise its not easy to diagnose thankyou kind regards J