I was in the hospital for 5 weeks at one point with an IV the entire time. My veins were sore and enlarged for a few weeks after I was finally discharged. However, the pain wasn't severe. I agree that if you are having severe pain you should definitely get it checked out just to be on the safe side.
I have a "go to" vein in my left arm, too. The last time I had a blood draw, the technician remarked that he could see "scar tissue" on the vein and said that I must have had a lot of IVs/blood draws (he has no idea). I wasn't too happy about that; some of my other veins have been a little trickier for IVs. I kind of need that one.
