Agree with usedtobeadoctor and needwait.
Are you sure you sent your EAD application in the correct address? USCIS has changed the EAD applcation filing address recently. You need to find the correct filing address from the latest I-765 Instructions at USCIS' website.
It is very weird that you do not get the receipt for such a long time, so you may re-file a new application.