Sorry to hear about your jammy situation (plum..jam..get it?). If there is any residual thorn left in your thumb, you may want to try one of my mums old fashioned remedies ! Gring some sugar and soap together (honest), spread liberally over the offending wound and cover with a plaster. This should draw any crap out. If you want to be a little more technical, you can buy a jar of mag. sulphate paste from the pharmacist, and use in the same way.
Of course, prevention is better than cure !