Not to scare you, but I my cousin was in the same boat and he is now three. I would take a test be sure.Also he is cute as a button, but unexpected. He was concieved in the first thirty days after the last shot. She had no clue.
Hi there. I am a bit younger then you but I might be able to help a little. Conceiving naturally in our late 40's is not very common. Even if your cycles were very regular, it is not the norm. Seeings how yours are still not regular, it is possible you have entered perimneopause. So chances are it's fine.
That being said, it can happen, so I would wait until 2 weeks after your last unprotected encounter and try a home pregnancy test then. Another alternative, especially if you are concerned about a prescribed medication is to have your Dr. run blood work. It would show in a blood test prior to urine sample. But again, it would have to be a ways past last unprotected encounter to be certain.
Good luck to you!