Q. My 5-month-old baby fusses every time I put her down on her belly. How can I encourage her to prop herself up so she can learn to crawl?
I've seen this in my practice: Some babies just don't seem to like being on their bellies! Don't worry about getting her to crawl just yet, as she's a little young for that (babies usually start crawling after 6 months). But tummy time is great for building muscles and preventing the flattening of the back of the head that can happen if infants are constantly on their backs.
Here's a modification: Sit on the floor with your knees bent, legs together, and lay her belly down on your legs so that her head is at your knees. You can play games with her by bending and unbending your knees or lifting your feet into the air. You can also lie flat on the floor and put her on your chest -- being close to you might make the whole belly thing better.
Another option is to buy one of those activity centers that she can stand in. (Not a walker, please -- they're dangerous!) Babies love to be upright, and she'll have another chance to strengthen not just her leg muscles but her upper-body ones, too. As she gets stronger and better able to push herself up off her belly, she'll probably fuss less.