I had problems with mine missing for months at a time but then it would stay for weeks at a time.. i was diagnosed as having polycystic ovarian disease.. (insulin resistant was my cause of it) but there are other causes, such as being overweight or genetic.
the major problem with having PCOD is that it is annoying never knowing when you will start or for how long plus the weight gain from water .. i lost 30 pounds and was prescribed low estrogen birth control pills.. it took 3 months on the pill to get me straightend out and i have had regular periods for the last 15 months now.
this is something you may want to ask your gyn to check with you.
If this is a new onset you should definitely go see a doctor. If your periods were regular in the past then it's important to check with a doctor to make sure that everything is functioning correctly. It is true that stress can delay your period, but 4 months is a long time. They will check and make sure that your thyroid is functioning correctly. If you don't have a normal doctor then call your local health department or planned parenthood and they should be able to help you out.
Are you having any weight gain? Are you more fatigued than usual?
You might have a cyst. This will cause a delay to your cycle. You should probably go and see your gyn on this.