small bump in mouth

I first noticed a rubbery bump that swelled up quickly within maybe 2 days, I popped it by biting down on it and it went away within a few days, week. I have now noticed small little smooth bums, same color of my skin, NOT open sores and was wondering what they may be. I have been stressed lately. Looking inside my mouth they are not very noticeable but when I put pressure on my bottom lip to flip it and see inside, I'm putting pressure on my skin and so they become a little more noticeable at that point. I can only feel a little sting on one which sits close to the corner between my gum and and the wall of my mouth although its actually sitting on the wall of my mouth.