Can i only get pregnant when i am ovulating? and how do i know i am ovulating?

Yes.: A woman has to ovulate ie release an 'egg' in order for pregnancy to occur. If you are having regular periods with cycles between 25-35 days then you are most likely ovulating. There are several ways to determine ovulation eg menstrual cycle charting, basal body temp, LH hormone surge (there is a kit),etc. The simplest way is cycle charting. Chart you cycles, 25-35 days are probably ovulatory.