Shoulder Problem

After 20 years of no exercise at all - I've recently started swimming again. It's been about 6 months since I re-started swimming, and I'm up to 3000 yards a day, about half of that is IM. The problem: About three weeks ago my left shoulder started popping. I'd say that it's popping out of it's socket, but it's more like when you crack your knuckles (or whatever you like to crack) :) Pretty much it does it all day long. If I straighten my arm to the side and twist my wrist - my shoulder pops/cracks. In the pool I've noticed (during crawl mostly) that my left shoulder (when I breathe to the right) feel like it's hyper extending. I've been trying to compensate by breathing to my left more, but it seems like it's getting a little worse over the last few weeks. Obviously I don't expect professional medical advice. But, it would help me to know if anyone else has similar problems or advice as to what exercises, stretches, swimming technique, or anything else that I might consider doing. All I can come up with is stretching more (I don't do very much), but I'm slightly worried that it's possible to hyper-extend it more (if that's what it is). I'm also considering spending more time on drills, and less on sprints for a while. I'm not in allot of pain. Mostly my shoulder is just uncomfortable all day long. The most pain, and it's not that severe, is in the pool. When it happens (and it's happened only three or four times) I stop swimming and start my warm down. Thanks.