My grandmother is 92. She can't walk on her own, only with support. She's more comfortable when some…

My grandmother is 92. She can't walk on her own, only with support. She's more comfortable when someone supports her left arm, meaning I hold her with my right. Today was a day of walks for her: a little walk to eat, another just to stroll, then to the bathroom. With my weight at 62kg, she probably weighs about the same. When she walks, she leans on my side and arm... I just got home, and I've started feeling a sharp, occasional pain, like a needle prick. It's in my lower left side, near the hip bone. Could I have pulled something when I helped her up from her chair and we walked? Or is it PMS? My period is due in 3-4 days.