What Causes Spotting Between Periods?

I am a 27 year old female. I have a normal pd cycle. I just had my last pd 2 weeks ago. Today i started to spot a lil i have no pd symtoms. At first you could only see blood when u wiped then it stopped a few hours later it got a little bit more heavy but nothing like a real pd. i am not on birthcontrol but when me and my borfriend do have sex most of the time we use condoms. Sometimes we use the pullout method. Could something be wrong with me? Or i been woundering if you can get prego but useing the pullout method. we have made no mistakes with that. please help