Spotting on Nuvaring

I spotted a couple of days before I started using this form of birth control because I was about to start my period soon. I put the Nuvaring in on the 1st and I continued to spot on and off until around the 12th when my period started. It lasted the right amount of time so I thought nothing of it. I took it out on the 25th like my doctor said and I started a whole new period 1 or 2 days after I took the ring out. It lasted a regular amount of time too. This is my second month on the ring and I started to spot again around the 14th. 5 days later I am still having that problem and no period. Is there something wrong with this situation or is my body just getting used to being on birth control??