It sounds as though there could be a couple of things going on in your garden. First, gerbera daisy (Gerbera jamesonii) likes a sunny spot, but it doesn't like much heat. Grow gerbera daisy in a bright location that's protected from sun during the hottest hours of the afternoon. Also, gerbera daisy is sensitive to too much moisture; take care to avoid overwatering it. It's best to plant it in a sandy or well-drained soil; if your garden has clay soil, grow gerbera daisies in containers, or amend the clay liberally with organic matter before planting the flowers.