I am 41, non smoker, very healthy, with normal regular periods. According to me my glow stats my most fertile day is 16.9%. 
In my annual exams there has been no reproductive issues identified. I have been TTC for about 8 months having sex within my fertility window but to know avail. 
Is 16.9% chance of conceiving standard for someone with similar stats or should I be looking to use fertility drugs? I am a twin and given my age I would love to have twins.