No matter how careful

you try to be, keeping a catheter perfectly set over two or more days can be a tricky thing. It never worked for me, the things seemed to shift/push-out the other side of the vein or whatever. I get a new catheter for every infusion, to me it’s ultimately safer that way and I strive to keep that site, as still and the muscles as relaxed as possible to help things along.
My own veins are sort of scarred and sore from all the poking, but again, my nurse will request to my neuro a port when the time comes.
You have gotten very wise advice from others here – including the rotating of the veins and being sure to hydrate. You might also ask your neuro about this reaction as he might suggest pre-meds or other alternatives to help you feel better overall during and after the infusion.
Hoping things get less painful in the future!