The leveling process takes time and everyone is individual. You don't seem too off track to me. I'll relate my experience thus far for comparision.
5-4-06 TSH was 6.4 MU/L (1-2 target range) - 50 mcg Levothroid prescribed
6-20-06 TSH was 3.7 MU/L (1-2 target range) - 75 mcg Levothroid prescribed
8-8-06 TSH was 2.7 MU/L (1-2 target range) - awaiting a probable increase in dosage
I was diagnosed about the same time you were with a considerably lower TSH. However, hindsight tells me I was probably undiagnosed for 10-20 years. I was very symptomatic when diagnosed. I am considerably better three months later, but fairly certain I still need more medication.
It seems reasonable to me it would take longer to move you the distance you need to go since it needs to be done gradually and you have further to go. Your body needs time between each increase in doseage to adjust (level) before moving the dose up again. I know how frustrating the brain fog and short term memory issues can be. I was so afraid that wouldn't go away. It has just been in the past week that I have felt that worry greatly lifted for me. I still deal with it to a lesser degree in the mornings until the meds kick in, but nothing like in the beginning. So I would say you'll start to feel greatly improved by the time your TSH is down to 3 or 4.
I'm sure you do feel terrible and I empathize. I want to offer hope, however, if you continue to follow the doc's orders, you'll be glad you did. Most of us hypos don't experience anything more complicated than this and the patience will pay off. Hoping that for you and me.
Hang in there and keep us posted on your progress. Just three months ago I had nearly every possible symptom. Today there is still some fatigue, some tingles in the fingers and the extra weight still won't budge, but I'm so very much better it is now getting really easy to hope.