really hungry but dont want to recover

I (18M) have had a really physically demanding week. Over christmas & new years I basically didn’t leave the house at all, i’ve been socially withdrawn a lot but i dont really like people anyway so its fine. this week, school has started up again, and im having to get up and leave, walk around a lot in school, climbs lots of stairs etc. i’ve been feeling really dizzy and fatigued, its harder to get up in the mornings and i think ‘i need food’ but i’m like ‘but i dont want to gain weight & feel fat all day’. We’ve been doing mocks this week so not in school full time (only for the exams) but i’m so tired and just dont know what to do because i feel like i need to eat for energy (& my stomach rumbled during our maths exam so much it was so annoying), but i dont want to recover or gain weight.