I Woke Up On Tuesday With What I Thought Was

I woke up on Tuesday with what I thought was going to be a pimple. Now it is very swollen and red and itchy. I'm not sure if it's a bite. It seems to be getting a little worse each day. It has a central point and then swells out and is red and swollen and itchy. Should I just let it run it's course or go and see a doctor?