There are a few reasons why your melons might not be as sweet as you'd like. First, make sure you're picking them at the right time - if you harvest too early, they won't have a chance to develop their full flavor.  If they taste like cucumbers, you picked too soon! You should also make sure your melons are getting enough sun and heat, as this is what helps them develop their natural sugars. Finally, make sure you're watering and fertilizing regularly to keep your plants healthy and productive.