When is the best time to have an exercise and diet?

Hello To All Mama's! Ask lang po kailan po ba pwedeng mag simula ng exercise like walking and squatting? Also food diet like lessening of sweets, carbs, and salty foods? My baby is currently 18 weeks and 4 days. To be honest, active kami sa mga nabanggit kong pagkain ngayon but I need to know when to control myself. Sabi kasi ng mga nakakausap kong mga nanay.. maliit pa naman daw ang baby bump ko. Masyado pa bang maaga para samin ni baby mag strict diet & exercise if ngayon namin sisimulan? We just want to aim normal delivery. You're suggestion and comments are highly appreciated. Thank you po mga Mommies!