I get periods every 3 weeks for last couple of years approx when rest of my life they were around 4 tyo 5 weekly, please advice why this could be happenin?

Many Possibilities: Without more info, it is difficult to know for sure. In general, a shortening cycle indicates a weakening ovarian reserve- decreased quantity & quality of the eggs that you have left. This is a natural part of reproductive againg. Other factors can be in play as well such as an ovulation problem (very common) so a visit to your obgyn or a fertility specilaist would be very helpful to you.