My son also had to have a reshaping helmet (just graduated 3 weeks ago after 5 months) and has been in PT for a year now through First Steps (early intervention in IN). I really think you need to have your doctor recommend PT again. If your ped. doesn't want to then you need to call whoever your state early intervention program is and have him evaluated, there is no cost to do this.
It sounds like he might have low muscle tone which is what my son has. He did an army scoot with one arm starting at 7 month old but didn't really crawl until his first birthday. He is now 14 1/2 months and isn't walking. He pulls up on everything but just won't take those first steps himself. We tried alot of wheelbarrel positioning with him, you hold the back part of them up and he hold himself up with his shoulders. My son hated this. I also hold him on my chest, face to face, and lay on the floor on my back and roll him side to side. This helps him learn to support himself when he falls (he learns to lean the other way). We also would sit him up and make him lean to the side and support himself with his arm. We also tried putting a towel/blanket under his chest/stomach and holding him up while trying to get him to stay on his arms and legs.
I never realized how these first "steps" at the key to soo many developmental things. Bacause my son hasn't been on his hands crawling his now will begin occupational therapy to work on his fine pincing grasp. The longer he goes without crawling/sitting and then walking the more he will get behind because instead of doing what he is supposed to do at 12 months he will be learning it at, say 16 months, so he has missed out on 6 months of walking and learning those developmental things during that period of growth.
Good luck to you and your son! Feel free to contact me with any questions as we have been there and are going through the same thing right now.