I'm glad you're feeling better! Out of curiosity, how hard of a gear are you using on your bike. Granted, your medical issues could fully explain it, but I wonder if your quad fatigue is a result of trying to push too big of a gear. You ideally want to be "spinning" pretty fast (80-90 rpms) and choosing a gear that allows you to do that pretty easily. It might feel weird t first, but it will help you go longer with less effort.
As for the mix of things, I generally think it's best for overall health and weight management to do a mix of resistance and aerobic training. Lifting may not directly benefit your cycling, but it will help you loose weight and feel stronger overall. Add in some rest days, walking and core work (e.g., yoga or Pilates) and you should seem improvement in now time. But be mindful of your body, too. Rest and recover when you need it. Eat well and drink lots of water.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher