How can you tell the difference between a cold sore and a pimple on the lip?

I feel exactly the same :( I have what looks like a pimple but I've recently slept with someone on a one night stand and got cold sores after even though she said she has never had one , I've had a cold sore in my childhood apparently most people get them and if you do it is likely to remain dormant in the nerves until something triggers it , if you've had a cold sore before you are likely to have the herpes simplex 1