spinning / rpm help

So I have been doing a lot of high impact exercise ( 5 x Bodystep , 3 x body attack and a combat class each week) I lobe the classes but am aware I will.be putting a lot of strain on my joints due to my weight. I tried rpm ( spinning) a few week ago thinking this would be good cardiovascular exercise without the impact but I found my bum hurt so much I kept trying to stand up, my hands hurt more than my legs at the end where I had been trying to take all my weight off my bum. I don't mean a little bit of pain I was in agony. Is this normal and is it worth me trying again

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