I have a bug bite (not sure what bit me overnight) that became hard, hot and itchy, and swelled up to baseball size in 8 hours. what do i do?

Several things: It sounds like you may have had a local allergic reaction to an insect bite. For the itching, you can take an antihistamine (Benadryl, Claritin, (loratadine) Allegra, etc) & apply 1% hydrocortisone cream to the area 2 x's a day as needed. Applying a cool compress may offer relief. If the swelling or redness or spreads or worsens, this could suggest infection & you should see your doctor.