>>1723585Depends, you'll need to give more specifics. Could be that your bike isn't adjusted correctly to fit you and you're in pain because you're straining to reach the pedals. Or you could be straining yourself by pedaling in too high a gear. Or if you're going on a hard ride without eating enough before/during you'll get very sore muscles.
>>1723583look at the Sheldon Brown article on servicing freewheels (you probably just need to replace that now since you lost a bunch of tiny bearings)
>>1723351more likely to be contamination on your cleat/pedal interface or something to do with your shoe
>>1723192https://www.youtube.com/watch?v=_dq3z_DybpI&list=LL&index=2 