I am a nurse and have a lot of injection exp. its not Ideal to use the same needle, I would avoid at all costs. what is important here is, did you clean the needle, perhaps with an alcohol swab prior to pinning with it? are you cleaning the injection sites prior to pinning? the introduction of a microbe is unlikely if you performed the fore-mentioned. signs of infection include: fever, swelling, redness, warmth etc. you will know if going to the er I necessary. this is stress you don't need bro make sure your stocked up so you can be confident.