Hi- I am really looking for some advice please?
I have started training (subsequently have not trained properly for over a year). I have been training for 3 weeks now 5-6 times a week with a combination of RPM classes (which I am new to), running, yoga,crosstrainer and some weights -nothing too heavy . I am alternating day to day what I am doing, cutting out snacks, and eating as healthily as possible. But today I weighed myself and I have actually put on 5 pounds??!! I can see my body starting to change shape , more toned and my belts are looser, I feel great albeit that I am working hard! However I feel at a loss to why I have gained weight, is this muscle as I am doing lots of cardio.. Sorry I am confused and would really value some help.
Thank you in advance

It sounds like the weight gain is muscle. RPM classes usually have some very high intensity bouts in them, which could stimulate fast-twitch muscle fibre development. How you run could have similar effects. Although most likely, the resistance training sessions are the primary cause. I wouldn't be bothered by it, though - you're feeling better, right? You're happier with your size, right? I'd call your current situation a success.

This happens to me as well and I notice the changes in my clothing before I see it on the scale. The scale will follow soon enough. Weigh yourself at the same time of day each time you weigh yourself. I think mornings are best.

don't know what the weight could be.. You could have gained muscle and lost fat, but that would have had to be quite the muscle gain in 3 weeks.. so I don't really think that. The most important thing, though, is that you feel good and that you look better.

A lot of people report that they start gaining weight when they start exercising. Has your diet been the same or have you been eating more? Often people eat more when they exercise since exercising makes you hungry, gaining weight would happen if the extra eating pushed your daily calories over in a surplus.. but then again, you say your belt is looser.

blood plasma volume does increase quickly when you start exercising.. but not 5lbs worth. It is possible that there are some water retention adaptions or something like that to starting training that could explain the weight gain.

EDIT:
and of course, like the poster above me pointed out, you need to weigh yourself on in the morning right after getting out of bed in order to limit daily weight fluctuations that depend on what you eat.

Have you increased your water intake dramaticallY?