I need help sleep training my 6 month old son!?

Within the pat 2 months, my son has gotten super congested 2 different times, and started rolling over (at first could only roll over one way so I would have to go roll him back) in his crib. Also, his bedtime got extended about 45 minutes or so. All of this led to him learning to fall asleep at the at bedtime and needing me to hold him, give him the pacifier and walk him around until he fell asleep on me in order to lay down for a nap. He used to be able to fall asleep on his own at naptime and bedtime. So now I am having to undo all of these bad habits that I have helped him learn. At 6 months, he now knows that I will come into his bedroom if he cries, and doesn't like being put down awake. My ped. suggested getting him really drowsy, laying him down and leaving for 5 minutes. If he was still crying, come in and soothe him however I need to so he will get back to the drowsy stage and lay him down again. Any suggestions for this? Advice? It's hard to listen to crying...