Post-ride weight gain could also be in indication that you're takign in to much water during a ride.

It seems like the OPs question really poses two issues: (1) why does her weight go up a couple of pounds after a weekend of long rides and (2) why she can't seem to get the scale to go down anymore.

With the respect to the first question, the explanation that it's water weight makes some sense, but that saide, it really makes me wonder if you're perhaps weighing yourself too frequently. Fluctuations of one or two pounds through the course of day or several days is pretty normal. There was a time in my life that I weighed myself at least once a day and found, in time, that my fixation on "the number" wasn't overly helpful. Have you thought about weighing yourself just once a week?

With respect to the second question, I would again suggest that you're not eating enough. I realize menopause affects your caloric needs, but I think your activity level warrants more food. Combine that with a very targeted approach to when you eat those calories, and I think you might see some progress.