Could Hard Itchy Lump Be Due To Insect S Bite?

Something bit me at night I felt it on Saturday morning when I woke up, it was just a small dot and itchy but over the past couple of days it has swollen, is red and feels hard. Everyday the swelling is getting bigger, on Sunday night it had become 3inches by 3inches and now by Monday evening it is 5 inches wide! It is red and raised and feels hard! I ve taken antihistamine and used antiseptic but it s not working, I m now going to get a Drs appointment, but any thoughts in the meantime on what I can do would help as I d like to avoid antibiotics. The bite is on my thigh. Thanks, Sarah