Hi.. Can understand your concern.. As per your complain a painful lump at the site of injection can occur due to inflammatory reaction due to irritation caused by the injection medicine leading to formation of a hard lump as a result of inflammatory process.. It can also be due to infection caused at the site of injection and the body s defence mechanism tries to wall off or confine the infection and there is formation of a small abscess which can appear as a hard painful lump.. In case if it has occurred due to inflammation it will gradually resolve itself. You can apply a steroid based ointment over it for reducing inflammation and pain.. You can take over the counter painkiller like advil or motrin which will reduce inflammation and provide pain relief.. Cold compresses can also be helpful.. In case of abscess formation antibiotic therapy and painkillers can provide relief.. I would suggest you to consult a physician and get evaluated to rule out the exact cause of the lump formation and get treated accordingly.. Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.