I agree that some weight training is still possible, and you may want to seek out a personal trainer who can safely guide you in this area. Have you had physical therapy for this? That may be beneficial in both resolving the issue and determining the cause. A PT can do a gait analysis on your walk and determine if it is a biomechnical issue (example would be over pronating). Hopefully if this is chronic you’ve had some therapy and have a few exercises and stretches that may help.
While you are anxious to get back into activities, you will most likey have to do so at a slower pace. Tendonitis takes time to heal, and you may have to try a few exercise to see what works and what doesn’t for you.
In addition to weight training, you may want to also consider swimming for the cardio conditioning. This is non-weight bearing and easy on the joints–your feet in particular.
In addition, it will help blood flow circulation which promotes healing.
I hope some of these suggestions help you. Wishing you a speedy recovery!