Getting Injured sucks! Plain and simple!
Its literally the worst feeling in the world.... and of course, its always the same story. Maybe you were lifting something over your head and your shoulders went, or maybe you decided to run some sprints that day and your hamstring cramped up like crazy; but no matter what type of injury occurs, you can always find a way to still get a quality workout in without messing with the current injured area.
For example, if your shoulder did tighten up from some type of overhead pressing then stop immediately... and I'm not talking about uncomfortability or burning from the workout, I'm talking about actual pinching pain. So if you are having pain, drop those weights and lets focus on some other exercises that will cut out pushing overhead, but still give us a great back shoulders workout such as: dummbell rows, face pulls, push ups (if no pain while doing them). There are a bunch of variations to use, but if these are hurting you too, stop immediately.
Although it sucks, getting injured is not the end of the world, so please don't beat yourself up. Even if you take a few days off, so what.... a few days, a week, heck even two weeks of not working out consistently is NOT going to make you fat. Instead, you're going to rest and recover, come back stronger, and get right back on track towards your goals!