If they are chiggers, you should be also getting the bites on your waist band and other tight clothing spots. Chigger bite bumps last a couple weeks too. Seems early for chiggers though.
I'd guess fleas or mosquitoes. Mosquitoes always go for my ankles and ears first for some reason. Mist your socks with OFF or some DEET based spray and see if the problem stops.
Change to a couple layers of really thin nylon socks and see if wool is your problem. I hike in doubled, super thin, nylon which are still thinner than one pair of regular socks and it works great. You are making me itch!