What are my Chances ?

I'm just curious if anyone knows what your chances of getting pregnant are if you only had sex on your first day of your fertile window?? My s.o. and I have been TTC for half a year and this month we only did the duty on my first fertile day due to having opposite schedules and all that!! I was having cramps that night and I'm hoping I was ovulating!! Is the first day of your fertile window too early to ovulate??