Will minoxidil will help with my generalized hair loss beginning with menopause and increasing after gastric bypass?

There are several medications which may help slow down your hair loss.  Minoxidil is probably not one of them however as I have rarely seen great results with it.

Hair loss after gastric bypass sugery is common. Nothing beats having a knowledgable physician review the entire story and examine the scalp up close. Standard blood tests are good of course but may not be sufficient in the setting of gastric bypass surgery. Potential causes with a story such as this include 1) androgenetic alopecia 2) telogen effluvium 3) chronic telogen effluvium 4) telogen effluvium accelerating androgenetic alopecia and a combination of the above. Other causes are also possible. See an expert.

The stress induced by acute weight loss and the surgery can bring out the balding genes if you have them and express them. The best treatment for this in a male is finasteride although there is no guarantee that it will work

It is clear that you have multiple factors affecting your hair loss.  It is best to see a hair loss specialist who can evaluate some recommended lab tests and review your history in detail, along with getting a full examination of your scalp to see what the best treatment options are.  Topical Minoxidil is something that may help, but there may also be several other treatments you can consider as well.  And usually an approach addressing all the factors involved may give you the best chances.  Good luck!!