I had one of those CT scans with an 'injection' (which is really more like a 'drip' as it's pumped into one's body) prior to my radiotherapy, so that they could make sure that the beam would be pointing at the right bits of me. I found it a slightly odd sensation but not an unpleasant one.
My previous CT scan was more interesting though, as I had to go into the hospital to be injected with a radioactive fluid and then return a few hours later for the actual scan. I was told to keep away from other people during the intervening period, especially pregnant women and young children, as I was radioactive. It felt very odd that lunchtime, eating a pub lunch normally but wondering if I ought to be glowing ;-)
I hope that the results of your CT scan show that it's nothing serious and that you'll be back home, fully recovered, very soon.