The spotting could be due to many things. Did you have any antibiotics? Did you take all your pills on time?
Burning while peeing can often mean you have a UTI or yeast infection. Is the burning happening when the pee hits the outside of your vagina, or does it burn before it comes out?
Do you have any reason to believe you may have an std? Did you have unprotected sex with anyone? If so, I would get yourself checked out for them just in case. If not, I would say it's probably just a UTI or yeast infection, but either way I would go to the doctor to be on the safe side and so you can get something to stop the pain you are feeling.