That whole sucking blister/ canker sore/no big deal thing made me feel so awful when I realized how painful it was. I switched pediatricians to another in the practice. She had referrals e-mailed to the children's hospital and a prescription for lidocaine gel within hours and an appointment set up for me with the feeding specialist for 2 days later. The lidocaine stings for a second and caused sobs, but the Magic Mouthwash UofM uses has equals parts lidocaine 2%, Maalox, and a benadryl type drug and my daughter had no reaction to it = wonderful stuff and made feeding her until the ulceration healed very easy, just dabbed it on with a Q-tip.
If your pediatrician doesn't aid you in getting appointments set up for THIS week, I highly recommend you find a new ped. Personally, I would skip the dermatologist and try to see a vascular specialist. If the Vasc. thinks a laser treatment is in order, that only takes 5 minutes and they can get you in(maybe my area is unique having a University and Children's Hospital on one campus along with outpatient office, but they all know each other and work well with each other once I managed to get in with one). It took a bit more planning to start propanol under observation.
I am NO expert, that is just based on my experience with ulceration. I had all my hopes aimed at finally seeing the dermatologist after weeks of calling for a closer appt., and within a minute after seeing her ulceration said "You belong across the street, I'll e-mail your info over so they have a head start, just make sure your pediatrician does the referral today." Maybe the derm can help you though?
In any case, good luck tomorrow and I'm sorry you had to go through the loooong weekend.