In-Process, means they are going to go through your application....
Now if everything is COMPLETE, they will move forward with the Medical Request/RPRFee. If something is missing or if there is some ambiguity concerning exp., academics, birth, marriage etc etc, you will be asked to provide further documents or proof. And the Meds will get delayed.
Medicals, RPRFee and Police Certificates might be asked for in the same Letter, and may be some other docs as well. BUT only if everything else is fine.
Anyways, considering if everything is peachy, in your case, look for Post (Letter) within 3 weeks or so.