If you feel 'fluish', do you want to eat much at all before a ride? Does it disrupt your sleep much? Up to 5 lb. water weight gain sounds normal but at least you know you lose it even though it is a bit on high side. (I think I gain 2-3 lbs. on water retention, and this is just from have salty food in meal and liquids.)
Have been in perimenopause for past 2 yrs. or so, but I only feel flushed for 5-15 min. several times ..a month. So I'm not the best person for advice. For certain, my symptoms are so mild that I wouldn't even recognize it while I'm pumping away on the bike.