Tips on bouncing?

I wouldn't say my fitness level is great but I do walk loads everyday. My boyfriend loves me bouncing on him and me doing all the work but after a couple of bounces I'm f*#ked it's like my legs get a massive cramp in my thighs wtf is going on? Any tips?

Any ways to make them stronger so I go for longer I don't know what to do or try as i really want to keep going to as long as I need it but right now that's not happening for me as my legs can't cope 😭😭