I had a son when i was 17 but has been trying to conceive for another one this past 16 years. and can't why?:

Conception: No one can determine the sex of your baby, but if you have been trying to conceive for 16 years consult a fertility physician for an evaluation.

Several reasons: There are several reasons for not being able to conceive, in 40 % it is a male factor and in 40-45 % it is a female factor. At this point, age is of a great concern. We observe a sharp decline in the woman's fertiltiy potential at around age 37. I would advise you to be seen by a fertility specialist as soon as you can.