Can running on my posterior tibial tendinitis make it worse?

Best for you to be patient and allow healing to maximally occur, as otherwise, this could exacerbate and make it more difficult to recover.

I believe you need the help of a sports medicine podiatrist. Why did you have this injury? From running ? What is to prevent from re injury. Muscle very important in controlling pronation . You need some control of this pronation . Anything from appropriate shoes to a custom orthotic to help control your injury. Strengthening very important. Not easy muscle to strengthen on your own.