48 years old with a body fighting me

I am trying very hard to fit exercise into my very busy scheduling being a certified home care aid. I have a right knee that was injured a couple months ago and then 3 weeks ago the dog knocked me down - on accident as we were playing ball, by bumping into my right side (weak side btw). After allowing time to heal, I started paying for personal training, and a couple hours after my 1st session my right knee was giving out on me, and didn't stop for about 4 days - no exercise, and only working - at home did nothing but sit on my rear and elevate my right leg. I feel defeated because I want to get into the best shape possible but every time I take a few steps forward, I literally get knocked down. What else can I do besides not eat and allow my body to use all the fat, etc stored. I'm not fat, I am chunky, and can't seem to get the scale past 192.