A: For one, colostrum is dairy-based, which can cause sensitivity; and two, it could cause interaction with the medication. Therefore, if you are taking the colostrum around the same time with the thyroid medications, it could interfere with the absorption. One way to overcome this would be to use a more absorbable medication. Tirosint is the one that's currently available, although it's only T4. The other option might be to use the colostrum at bedtime to see if that makes a difference for you.
The other thought that I have though is that you could be sensitive to the colostrum. I've had a love-hate relationship with colostrum because it has so many benefits, but I worry about people being sensitive to it if they are really dairy sensitive because there may be potential for some cross-reactivity there with some whey or casein. I haven't been able to find a lot of good information on people who are dairy sensitive and are able to use it. Dairy sensitivity is very common in Hashimoto's.
Having said that, although it is generally recommended to stay off dairy indefinitely, I’m working on reversing dairy sensitivity, so be sure to stay on Thyroid Pharmacist's email list for updates.
Colostrum is great for healing the gut. One idea that I actually like to utilize for gut healing that works like colostrum is serum based immunoglobulin, which is dairy-free. Orthomolecular Products makes this supplement, and there are a few companies out there that make it as well. The one I've used with a lot of success is Orthomolecular Products, and you can get this in a powder form, so you could use it in the same way. Just to be on the safe side, I would space it out from thyroid medications by two hours, maybe even four hours.