hi i was on antibiotics about a month ago and so i stopped taking the pill for a week and my menstrual cycle started then the night it started i started the pill again in week two. im now in week 4 and meant to be menstrating but im nt should i be worried

No, no need to worry. It is just a strange way to take pills, so please be sure to follow the directions next time! Your cycle is just trying to adjust itself from the sudden stop of hormones, to beginning again at mid-cycle. Your cycle will probably take a month or two to adjust.

Why did you decide to stop taking your pills? Antibiotics can cause your pills to be less effective, but it is not recommended to abruptly stop taking them. When you stop taking the pill for a week, you essentially missed 7 pills in-a-row. What you needed to do was to start a NEW pill pack after your period started; not to start again with the middle of your pills (in week 2).

I you have not had unprotected sex, then there is no worry, and your cycle will regulate itself again.