I am having lots of difficulty with my tomato plant. It will look very health in the morning and after a few hours, start to droop completely. I am using a self watering pot and keep it filled. I thought I might be under watering and started watering more which just didn't make a difference. What am I doing wrong?
There can be multiple issues with potted plants in general.
If the pot is too small or it gets too hot there or if the soil in the pot is too compacted and the water just goes around and comes out the bottom and it doesn't actually get to the roots. There can be other issues too like the plant doesn't have a good root system for some reason and so it cannot absorb enough moisture during the hottest part of the day. And even more fun could be disease problems.
So to provide a better answer it would help for us to know what kind of conditions, how big the plant is, where you are at, if you've repotted it, how much it gets watered, etc.
Remember the more details you give in your question the easier it is for people to answer. :)