I broke out in hives/rash today. It affected my hands, arms, back, and scalp at first. I went to the clinic, got a shot of cortisone, and it was relieved, but never really went away. Now, about 6 hours later, the hives have lessened on the former areas, but are spreadinng to thighs and my tongue has a swollen area. My throat is in discomfort; it feels similar to acid reflux. Im scared that my throat will swell when I go to bed or something.
What should I do?

You should phone the clinic immediately Nd make them aware of your secondary condition. We can't diagnose of advise over fhe internet