Hi Jen,
Exposure to allergens weakens our immune system and over time a weak immune system launches an inappropriate, erratic reaction that targets our bodies own cells. Exposure to allergens can also trigger flares and worsen symptoms. Studies show that an increase in immunoglobulin E caused by the allergic response is associated with worse symptoms.
I had a similar problem when my husband first snuck in our first boxer. I noticed that symptoms were worse when my seasonal allergies also kicked in. Limiting contact with the dogs (the number of dogs has grown over the years) when my seasonal allergies are bad helps.
You can try the common approach as you mentioned, which is to limit exposure, have your boyfriend brush the dog outside, keep the dog off furniture and out of your bedroom if possible (or keep him or her in a portable kennel especially at night), don't let him or her lick you (encourage him to play with toys not your arm) and if possible keep him outside more. Sometimes, people become acclimated or sensitized to dogs they're allergic to.
And sometimes, people are allergic to only certain breeds. I'm more allergic to short hair-dogs and skin tests confirmed this. It may be that you would do better with a certain breed. Or perhaps your dog can temporarily spend more time at your boyfriend's.
A common approach with block and replace is to keep the initial starting dose the same (with methimazole it's usually 40 mg) while adding the thyroxine. This works the same as lowering methimazole. Then, over time, as your FT4 falls, the dose of methimazole or sometimes both drugs can usually be lowered.
So your current protocol isn't unusual. It's just that with exposure to allergens your immune system is being stimulated and you want to strengthen it, rather than stimulate it. Immunomodulators like plant sterols and sterolins, antioxidant vitamins and German chamomile can help.
It's also important to take antihistamines to help control your allergic response. The new ones like Claritin, Zyrtec, and Clarinex don't cross the blood brain barrier and are safe to take. You shouldn't take ones with stimulants like pseudoephedrine (Sudafed). It could be that controlling your allergens with antihistamines and other lifestyle changes will allow you to keep your dog and still heal. Best, Elaine