Be aware of your own limits and stick to them: you may feel bad, tired, sad. In this case, you have the right (even the duty) to set limits in the help you can give. If your friend makes a request that you don't want to answer, you have the right to refuse, but this does not make you a bad friend. You can offer help that suits you better instead.
I can see that you are not well at the moment, but it has been difficult for several weeks for me too.
I'm not sure I'm the best person to help you.
If you agree, we can research who we can turn to for help together.