I am sorry you are struggling this way, I can relate to what you have described "feeling". You probably "give" in the way you wish you could get yourself too.

Does anyone EVER tell you what a wonderful teacher you are? Has anyone ever given you respect? It could be that because you DO help others in your teaching that people around you think you are stronger than you actually are too.

Often these "negative feelings" develop in one's childhood and the person isn't even aware of it. This is probably part of how you teach your students making sure they don't beat themselves up if they don't "just" get things right. It may trigger you when a student struggles because somehow in your past you were blamed when someone else was struggling. I am not good enough because YOU are not good enough messages. Or, I am not happy and it's YOUR fault messages too. And even if you don't do what I want and need you are being bad. Even, if I don't think what you care about is important that what you care about isn't important. That's one children often hear a lot. This can create this ongoing challenge in someone where they begin to subconsciously believe that their feelings are not important and don't have any value. And even "it's more important that others feel good about themselves".

Does this describe how you feel at all?