Do some basic stretches daily,nothing to hard,just enought to limber up,also if you do a lot of hills,the fact you cant drop into a faster cadence could be the problem?Just like buildng muscles,the harder the pedalling the more likely it is you will build muscle,you need to be able to lighten the effort when things start getting harder,so gears would be the best way to go in my opinion.Light and easy ie spinning will shape,but hard and slower,will build,so get some more gears,and start making it easier to spin.