It could still be lice. My grandson was "checked" by the school nurse a few months ago during an outbreak, declared clear, and it turned out his itching was, indeed, lice. She was apparently not trained to see the nits, which were close to invisible in his medium-brown hair.
When my daughter told the nurse a couple of days later that grandboy was infested, she became angry and defensive. Not terribly professional, unfortunately. But I hope you'll tell your school nurse if it turns out she was wrong; you may have a better experience than my daughter did.
Check pictures online of what to look for, and do a close inspection yourself with a flashlight. My DD took her family to "Lice Knowing You" and got everyone inspected and treated with natural, non-toxic oil. They do a free follow-up check and treat again if necessary (it wasn't). All has been fine since – no more itching.