pimple or cold sore?

So before my period, I get a little bit of acne (nothing I can't handle). It's in the corner of my lip and I have never got it there! I have never had a cold sore before. It was a one big puss, but it really hurts and it's having a hard time healing because it's on the crest of my mouth. But I'm freaking out because I'm not sure if it's a pimple or cold sore and I have been giving my boyfriend head😖 someone help?