Your cycle pattern definitely sound abnormal. Your frequency of having sexual intercourse will not effect your periods. Thus, whatever is causing your skipped periods is independent of your sexual activity. Skipped periods are often due to cycles in which ovulation does not occur (anovulatory cycles). One of the most common causes of these type of cycles is polycystic ovarian syndrome (PCOS). This syndrome is caused by an abnormal endocrine system in which hormones are secreted abnormally. Women tend to be overweight, have diabetes, and occasionally have facial hair growth. Sometimes the skipped periods are the first sign. Another possible cause (that doesn't seem to apply to you here) is excessive exercise and weight loss
. If you are training for a marathon or something similar, this could explain your skipped periods.
I suggest that you schedule an appointment with your OBGYN. Bring with you a calendar of when you have had your period over the last year. I you don't have calendar yet, start making one. Your OBGYN can discuss the possible causes of your period problems with your personal past medical history in mind. You can get any necessary blood tests done and get a step closer to figuring out what is going on.