Waalaikum assalam! Honestly la, a few of us mommies took our booster in 3rd trimester juga, some even later, and babies turned out fine, doctors usually say it's safer to take it than to skip it, especially with your conditions. Since you have GDM, low Hb, and low platelets, I'd really suggest checking with your OB first before you go petang tu, just to make sure they're okay with the timing and dosage given everything you're managing. Most side effects are mild (arm soreness, slight fever) and not specific to 3rd trimester, tapi better safe than sorry with your pregnancy situation. Let me know what your doc says!