Bone cracking sounds?

Hello.. i used to have a lot of back pain but i started advanced exercise i made many muscles around and it stoped. but now while im using the pc and sitting a lot its starting to come back, when i was a kid my only passion was milk everything i eated had to be connected. so my bones was iron i could jump biuldings, had many accidents and i never broke anything, but then milk strangly affected me.. i had headaches for 2 months and i didnt know it was from milk, so i changed my diet, became better. i did 17 years of martial arts some bone areas as legs, pounch are powerful enough to brake anything. since young age i always hit hard stuff that way i turned those bone areas more powerful. but now sometimes even if i make a move i hear a joint making a cracking sound, and i have these everywhere on my joints it dosent hurt but no matter what i tried i dont see any changes.. it all started when i stop gym for a year. doctors told me is from too much hitting. cave me some pills but no changes.. can anyone help please?  

Many thanks
John