What are the real chances of getting pregnant from precum both on the pill and off of it?

My boyfriend NEVER ejaculates inside of me, only precum.

I am on the birth control pill but it makes my periods very light and I often don’t get one which can sometimes stress me out.

I made an appointment with my doctor to discuss different BC options but in the mean time I don’t know why I stress out so much when I am on the pill and my boyfriend has never finished inside of me once!