| I second the advice of one responder that you should read up on exercise/training principles to get a better grounding.
My diagnosis as a diabetic and my meds have not affected my muscle tone, but getting into an "exercise rut" has that effect. By exercise rut, I mean doing the same routine for a while such that my body has adopted to it and has stopped responding or I no longer exert as much intensity as before. So, I modify my routine every 2-3 months. This doesn't necessarily require a complete revamp of what I'm doing, as sometimes making just 1 or 2 changes every now and then can make a lot of difference. Hence, if you lift weights, increase the weight, increase the sets, change the sequence of your exercises, or replace a couple of exercises; or even adopt a new set of exercises every 3 months.
You can also try new activities. For instance, if you work on machines all the time, why not try free weight? If you do a particular type of yoga, why not try another type? | 
