I don't know how much protein you are getting but maybe increasing the protein could help. Riding a bike might also be beneficial as way to take a break from running. Have you tried using the workout generator and doing body weight exercises (pushups, planks, squats, bridges, bridge ups, etc.)?
There are different ways to do pushups that could make them more challenging. Maybe start with the workout generator and see if that can help you figure out some kind of routine to start out. That's what I did when I first started doing strength training (with gym equipment). Then, when I decided to do it at home instead of at the gym, I went through the workout demo (see the links below) and picked out ones that I could do. I made sure that I picked out ones that would make up a full body workout. You could start out with some of the more basic exercises and then as you get better at them (gets easier, not getting fatigued, etc.), you can go to the more advanced exercises. I think a lot of it is figuring out what works for you and working from there.
I hope this helped.
Workout Generator: www.sparkpeople.com/resource/fitness_plan_
Upper Body: www.sparkpeople.com/resource/exercise_demo
Lower Body: www.sparkpeople.com/resource/exercise_demo