light headed 😴

i am 15+4 & i have been getting light headed lately. from doing things like standing up too long while im cooking & taking a shower. with the cooking it doesn't happen often at all. but the shower it seems like it happens every time. i cannot be in the shower for over 10-15 minutes, i get extremely light headed almost like im going to faint. at first i thought the water may just be too hot. now i make sure the water is warm, but more towards cold just not freezing & still today as well as other days, the same thing. idk whats wrong or what it could be. ive been taking my prenatal vitamins. has this happened to anyone else?