I also have self cathed on and off for the past few years. I went through a period of around 6 months when I was unable to pass urine at all and needed to use the catheters every day but now it's only now and then.

I never did perfect the technique and managed to give myself several infections. Blood in the urine can definitely be an indicator of infection, but also of trauma. If your catheter is too big, than than can cause trauma, so can the way we use the catheter when we're learning. I always use the smallest bore than I can manage ... and for me that's a size 12FG

I take daily Cranberry capsules whenever I'm cathing to help prevent infections. They won't cure an infection once you have one, but they can help with prevention.... so can absolute cleanliness and lots of oral fluids.

If you notice blood again, or if you experience scalding, bladder pain, back pain, urgency or fever, please contact your doctor as you probably have an infection. In the absence of other symptoms, a few specs of blood probably won't hurt as long as it doesn't doesn't increase in volume or continue more than a day or too..

I hope that's helpful in some way.