Bite marks on my skin, but cant find any good reasons for it, please help?

So i noticed that i have these bite marks on the bottom of my legs and on my arms. I dont have fleas and i cant see any external creatures crawling on my skin. The bite marks are pretty small and usually only annoys when im in the shower. I get these biting sensations sometimes when im in the shower. So does anyone know what this could be? Any help would be very much appreciated!