I am 20 years old and my husband and I have been trying to conceive for 18nw months now. I was on the shot for five years and the pill for two years.?

Visit the Doctor. There are a number of reasons that a couple may have trouble trying to conceive. There may be hormonal imbalances or structural lesions that make fertilization and/or implantation of a fertilized egg into your uterus. There may also be abnormalities in your husbands sperm. Your ob/gyn can help you pinpoint a cause & help you determine the next steps, as well as get you set up with prenatal care!
Be checked. It sounds like you should both be evaluated. Certainly the long time you were on birth control is a point, but presuming that they are out of your system, if it has been over a year of having regular intercourse at the time of ovulation, you should be checked. That said, if you have not been taking vitamins, and doing basal body temps, then do that first.