post sex sadness

Hey I lost my virginity yesterday (16) and a little while later i felt really blue. I went shopping after and i didn't even want to buy anything (which is nothing like me). i was really quiet and kinda melancholy. i googled if it could have to be related to the fact i had sex. Turns out it that there's a few different reasons why and i think mine is that i just wasn't ready even though i thought i was. i don't know if i should tell him or not even though i know he would be understanding to it. Please help and also lmk if i'm not the only one that has experienced a sad feeling after sex. thanks💗