I'm 32 and afraid i'm in premature perimenopause. hot flashes/night sweats, brain fog, fatigue, mood swings. tsh 4.0. on hbc. how can i know for sure?

It's possible: 32 is young for menopause, but possible for various reasons. Are you having periods and if so how often? Your doctor can check your gonadotropin levels to tell you if you are perimenopausal; if so then further work up would need to be done to determine the cause. It is important to note that your symptoms could also be caused by other medical reasons so it is important to follow with your doctor.