I have a couple of fungus spots on the skin in the groin area. The doctor prescribed ketoconazole cream and fungus became much bigger and redder. Should I stop using that cream? Am I allergic to it? What should I do?

Difficult to know. Without seeing the eruption cannot tell whether this is candida (yeast) or a superficial dermatomycosis (skin rash like athlete's foot). If it is the latter ketoconazole will not be effective. See a good dermatologist.
?allergy. Assuming you had tinea cruris, or jock itch, Ketoconazole Cream would have been an appropriate therapy. However, it does sound like you may be allergic to a component of the cream that was prescribed. This is particularly true if the area is now itchy and weeping red. See the same doctor again and have them evaluate you and prescribe another medication which you can use.