Perhaps your boss does not want to overload you with work on your first few days. I think things should be back to normal after 2 weeks? Dont be too hard on yourself, give it more time.
In my case, it's not my colleagues taking over my job. My boss employed a new contract staff to take over some of my duties while I continue to access emails from home. When I'm back, the contract staff handed back to me the work and I've kept myself up-to-date via all the emails, so no problem catching up at all. Think I took about 1 week to fully take back the work.