Pop sounds usually means that there are nitrogen escaping from your joints. Usually possible when u clentch your hands together. Pretty harmless in the short run, might be harmful in the long run.

Crack sounds your joints are screwed, must immediately seek medical attention.

In this case, I agree with Jones. Do seek clarification from doctor.

I had only one or twice pop (mainly on my shoulder) in the my very first and second work out after that it totally disappear.

However, your case it seems to be very frequent. Better safe than sorry.