A. Now that babies are put to sleep on their backs, which is very important because it significantly decreases the risk of sudden infant death syndrome (SIDS), they get less tummy time, so it's not surprising that yours gets frustrated when he's on his belly during the day.
That said, some supervised tummy time is important, too. It helps to strengthen the muscles in the arms, neck, and trunk, gets babies ready for rolling and crawling, and prevents plagiocephaly, the temporary flattening of the back of the head that can occur when a baby is always on his back.
That said, you don't need to make your baby miserable. A few minutes of tummy time each day is fine for a start -- and you can make it a game by getting on the floor with him, face to face, and talking to him (I loved doing that with my kids when they were babies). Put toys that he enjoys in front of him. If he's not rolling over yet, he may feel more comfortable if you roll up a small towel or blanket and put it under his chest for support. You can also try resting your infant on your thighs with your knees bent, so that he's upright on a slant (some babies tolerate that better).
As he gains strength and you figure out ways to entertain him, he'll be able to stay happily on his stomach for longer periods of time, and you won't have to try so hard to get him there.