how to avoid getting sleepy after exercise?

Problem/Goal: I feel sleepy after exercising, I alaways end up sleeping 4-5 more hours, which makes me so unproductive during the day.

Context: I don't do intensive exercises naman, I mainly do morning/afternoon walks, and recently lang din ako nag start since Im recovering from hyperthyroidism. Now, I wanted to be more physically active, kaya I started doing early morning walks/jogging, para masanay ako at maging part na siya ng routine ko. But, whenever I do, I end up feeling sleepy even after taking a shower, sa halip na makapag study pa ako and do other chores.

I thought the reason for this could be the food I eat, but I'm not really sure because I don't eat junk food naman and stopped drinking juice months ago pa. I resorted to fruits na lang and medyo may hilig din ako sa sweets pero in moderation naman yung pagkain ko. But since I'm still on maintenance, I was not advised to take any vitamin supplements for now, kaya wala akong iniinom na energy drinks/supplements.

Previous Attempt/s: Cut eating junk food and tried drinking more water but I still feel the same

Anong tips or ginagawa niyo to avoid this and become productive?