Why do i sometimes feel weak and nauseous when i am ovulating?

Ovulation : Ovulation involves rupture of an ovarian cyst (follicle containing a mature egg), and the escaping fluid may irritate the intestines, or the rupture itself may cause nausea, depending on the sensitivity of the individual. On the other hand, if this is just "occasional", and you may not actually be ovulating, see your gyn provider as the nausea may be from intestinal disease, and only coincidental