Sounds exactly like my ds at that age, when he cut 4 molars at once. It went on for about 2 months and the worst part of it included what you described in adition to 2+ hour nightwakings... not fun! I used to wonder what had happened to my awesome sleeper? just when i thought i had given a round to sleep training i seemed to be back on it.
What i did was using pain meds before bed, ask the ped for stronger combos (he ok'd using both, tylenol and motrin on awful nights) and be super attached to my schedule. Your prior crisis schedule sounds great to me and you have to repeat to yourself that you're not doing wrong and that things are not gonna get worse. I was often disturbed and afraid of what was about to come, was my ds gonna forget how to sleep properly? was he going to be waking in the middle of the night from now on? The truth is that with the correct routine and intervention, a sleep trained little guy can't forget how to get back on track. Yes, it might take a while and things might seem cloudy for a couple of months, but it gets better.
Molars do that kind of things to little ones, they seem perfectly happy and joyful during daytime but come bedtime and they become bears and then crankiness due to lost sleep and overtiredness shows up to the mixture and you have one messy household.
By all means and as much as you can, try to extend the nap whenever he wakes cranky or crying. That means he still need his sleep but can't keep going. Sometimes molar pain prevents lo's from deep sleep. Is not a torturing pain but more like sand in your shoe... it bothers, you know it's there and you can't be comfortable but it's not like you're going to die from it. For that kind of pain, I have found that longer winddowns (say, adding5-10 mins to your usual routine), extra cuddles, being there when they're fussy during their sleep, help them get more relaxed and hence, getting to the deep sleep phase they usually reach without much help. Just like you need a hug or a cup of hot tea after a bad day.
Let us know how you get on with this tips and if there's anything else we can do to help you. We've all been there and will be happy to help!.
Good luck!