What Causes Spotting After Periods?

Hi, I had my period about 2 1/2 weeks ago and about 5 days ago I started spotting, it was light pink and this lasted for a day and went away, 2 days went by and nothing was there, then the 3rd day I started spotting again and it was light pink then I checked again it was brown. This morning I woke up and I was bleeding heavily but has slowed down through out the day. Not sure if this is my period again, an infection, or possible that I am pregnant? I never have spotting, what could it be? I did have a UTI not too long ago and I took antibiotics, then I think I had a yeast infection follwing the UTI because I felt a burning and itching sensation but never went to the doctors because it went away. Any advice? Thanks for your help!