New to Low Carb

I am new to the low carb lifestyle. I have now attempted this approach a few times, and have some major body responses that make it very hard for me to break through the first week or two.
I have hypothyroidism, and was up to the maximum dose of synthroid before I began to gain major side effects from the medications. The doctor agreed to lower the doseage, but he wanted me to drastically change my diet as a tradeoff to the med. In essence, the only foods I would be allowed to eat would be meat, vegetables (including starchy veg other than potatoes), eggs, and nuts/seeds. I discovered it was very similar to the Paleo Diet. However, I was not able to eat sweet potatoes or fruit. The problem was that I would hit a massive wall about 3-4 days in (major heat flashes that lasted a long time, headaches, exhaustion, difficulty concentrating, memory difficulties, general grouchiness :-/. When I thought I was past this wall, I would hit it again about a week or so later. The problem was that I would get migraines so severe that I could not function at all for several days. I finally gave in to bread, and the migraines disappeared. The thing is that during this couple of weeks I experienced amazing weightloss that came back once I caved in to breads again. Have any of you experienced this? How do you break past that point of the body putting up such a fierce fight? I would welcome any and all thoughts and suggestions that are shared through similar experiences!

Journey
330/320/155