So ever since I stupidly tried a rear delt fly on the pec machine while sitting sideways (to get a bigger stretch) I have had this ache that comes and goes on heavy eccentric movements or if I twist suddenly.

To be honest it hasn't really hindered my progress and I've actually still gotten stronger. Up until two days ago where I tested my overhead and felt a sustained aching as I lowered the weight. I took a day off to feel if it got better but today on lat pull-down I felt the same ache as I lowered the weight as well. I don't really feel pain in an idle position but I am concerned that I aggravated it or worse. Any ideas what it might be? Obviously a doctor would be the next step. Note that as far ad anatomy I'm a novice. Thanks.