I have struggled with this tryingtobeme; and for me it's because I'm highly sensitive and can feel when someone is unwell and/or struggling. To alleviate those feelings I try to "fix" things for the other person. This leaves me feeling drained and normally doesn't result in the other person doing better, so it's a never ending cycle. I have gotten better at recognizing my behaviour and a therapist pointed out that I over function with others. For me this is a function of not feeling good enough about myself, so I try to compensate for this. This just reinforces that I'm "not good enough" because I feel used by others.

The first step to changing a behaviour is recognizing it. You have done this. Now the next step is to work on changing your behaviour. Hope that helps.