After I flush my toilet the water level in the toilet bowl itself is always very low. How can I fix this issue. Thanks!

Check to make sure the little tubing that runs from the ballcock is connected to the white overflow tube. This is what fills the bowl.
Good luck, Tom

Thanks Tom, but not the problem... the bowl fills fine, but then once in a while... two of my toilets have very low water... like something sucked the water down the drain.