TTC #4 and thyroid

LuLuNew • I have 3 amazing kids 8,5, and 15 months and we are ttc #4!! My husband is in th police academy and about to graduate!
Does anyone else have troubles with getting pregnant w siblings? It's been easy and fast to get pregnant with the first 3, now we're trying for #4 but now I have a underactive thyroid and taking medication for it. Does anyone have advice or is also going through this?