A painful limp on top of the big toe can be either an infected ganglion cyst or a boil. It can also be a bone growth. An X-ray of the big toe and neighboring foot should be done. Also, the podiatrist may be able to diagnose this by clinical examination itself. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.