Why do my bones crack?

It was never so bad but now everytime i move my arms crack. same with my knees, and when i'm sittin im sometimes have a hard time getting up and when i do my lower back just cracks but it feels realy weird? I don't consider myself overweightt too much, maybe like 5-10lbs? but like i said its only got bad for the ped like 2 weeks? does anyone know what it is?