If your pregnancy test is negative, you are not pregnant. A late cycle means you did not ovulate or you ovulated late this month. That causes the cycle to be abnormally long. It does not necessarily mean that anything is wrong or that you need to do anything different.
If you are only 20, I doubt you are having trouble. The definition would be lack of conception after a full year of trying. That would also include using an ovulation predictor kit for at least 3 months first. They are over the counter. You can mention it to your gyn but it is early to be concerned. Only about 60 percent of couples conceive in the first six months, the rest conceive in the second six months. Very few are infertile.