Child has been achy tired unwell since covid

my daughter got covid early jan. had it bad for one day only and recovered quickly. she has since become a different child. tired emotional*achy and complaining of joint pain and severe back pain.

today she had a red patch near her spine come up on her back. her back pain has become so much worse and she can barely walk. all vitals fine blood test was cleared . everyone can not understand what is wrong and what is the patch it doesnt look like any type of rash.