How would I know if I have fertility issues as I am not with my husband for several months. Iam 40 and never had a baby. Please help.?

Evaluation soon. See a fertility specialist or a general obg with good fertility skills. Getting evaluated is the only sure way to know if there are problems, and at age 40 the sooner you find out the better your chances of success will be.
Hurry. Unfortunately, age itself can reduce fertility. The conception rate in women 40 and older are about 10% per cycle at best and a much higher miscarriage rate. I would encourage you and your husband to have some preliminary evaluations such as, semen analysis, ovarian reserve testing, uterine and tubal testing. Good luck!