Why are my legs really itchy after shaving?

My legs get really itchy after I shave them and I can't figure out why. And they stay itchy till I shave them again. I used to use a Gillette Venus razor a few years ago, and my legs got cut up a lot and had little red bumps over them, so my dad gave me a Gillette Fusion razor to see if that helped, since it's for the face. It helped for a bit, but after a while my legs would get itchy again. I've switched back to using a Gillette Venus razor and I change the blade part once or twice a month. I've tried using men's shaving cream, women's shaving cream, unscented soap (I never use scented soap), body wash, shampoo and conditioner. I've tried to only shave once a week to see if that helped, but it didn't and since it's getting warmer, I'll start shaving more often. I've tried waxing (had it done professionally and I've done it myself) which resulted in red, itchy legs for a week. I've never had good results with Nair, I find it doesn't remove the hair very well. I try not to scratch my legs, but sometimes I can't help it and sometimes I've scratched my legs till they bled a bit. I don't know what else to try or what could be causing this.