Did I suddenly develop a dairy allergy?!

So here's a little background..

I'm an 18 year old male and have never really had any major allergies before in my life (pollen, seasonal) to name a few. A few days ago (Friday) I was sitting in class and all of a sudden started feeling really itchy (I had a ham and cheese sandwich for lunch). The itch started on my scalp and ears and spread to my back. When I got home, I took some benadryl and went to sleep. The itchiness was relieved for a few hours, but when I ate dinner (casserole with cheese) it returned and was even worse than it had been before. Again, I took some antihistamine and went to bed. I got up the next morning and ate a bowl of cereal and started feeling itchy again. This time, I had big puffy hives and a rash. This same phenomenon has continued seemingly after every time I consume dairy. Last night I had a cheeseburger and milkshake and the hives and rash were the worst that they had ever been. Today, I woke up with a small localized patch of hives and when I ate my bowl of cereal, they puffed up again (This time everywhere on my body). Up to this point, I have never had a dairy allergy. Could I really have just spontaneously developed when at this age? Is this even possible?

Thanks for all the answers...