Hi,
Considering the history you have given this could be henoch schonlein purpura.
This is happens due to inflammation of blood vessels and can be associated with joint pains and pain abdomen.
Usually preceding history of sore throat will be there.
This can require a bit long term treatment and certain blood tests need to be done like cbc, esr, aslo,
crp , rft and urine routine microscopy.
You can get back to me on practo consult as i need further details and to treat you.