My mom had stomach cancer surgery in november. is not doing chemo..her blood pressure is 91/60...why is it so low & what does this mean?

Low bp: There are some common reasons for the low blood pressure. First make sure that she is eating and especially drinking well. Dehydration is a common cause. Also if she is taking pain meds, these may cause low bp, or any combination of these two factors.

Hard to say: Since surgery was several months ago, it is probably not directly related. 91/60 may be a normal blood pressure for some women - it depends on what your mother's baseline is. If she feels ok otherwise it might not serious. But if she is not feeling well or looks sick - give her plenty of fluids and head to your nearest er.