How can I tell the difference between a sore pimple or a cold sore on my lip?

I sometimes get a pimple on the edge of my lips, but I have one that's pretty sore, so I need to know how to tell the difference between a pimple and a cold sore. I've never had one before, but my dad gets them and I've heard they're hereditary. If it is a cold sore, are there any good remedies that don't cost a lot?