Oo, normal yan ate! At 4 months, marami pang babies na nahihirapan mag-lift ng head consistently during tummy time kaya parang tired o frustrated lang sila, lalo na kung kulang pa sa neck strength. A few of us tried just doing short sessions muna (like 2-3 minutes lang) and breaking it up throughout the day instead of one long stretch, at nakita namin mas okay ang babies namin na hindi ganong stressed. But honestly, if you're worried na may developmental concern or kung talagang struggling siya more than expected, best to check with your pedia just to be sure, ah? They can assess if lahat ay on track lang talaga.