What does it mean when you feel jittery when you take pre and post workout supplements? is it safe if you are sensitive to caffeine?

Depends on supp.: There are many pre and post workout supplements. I imagine many of the pre-workout supplements contain caffeine and thus are best avoided if you are sensitive to caffeine; but there are probably some that don't have caffeine so check them out. Generally if you are jittery after any supplement i would take it as a sign that it is not a good fit for you and you should find one that does not do this!