Is this irritation or head lice HELP?

I work in education with children with special needs, some come from poor families with bad hygiene, hence head lice. I caught head lice at a different school I worked at about 3-4 years ago and got rid of it. Since then I have put tea tree oil in my shampoo bottle which is supposed to be a deter ant to lice from wanting to nest in your hair. I put about twenty drops of the oil in my shampoo bottle when I first buy it and shake it up pretty good before I use it so I don't get all the oil in one use. This week my head has been really itchy again, with red patches no larger then a sesame seed on my scalp, I have been wondering if I have caught lice from a student again. I have been looking for nits and haven't seen too much hard evidence yet, or if I might be having a reaction from the tea tree oil in my shampoo, causing my head to itch and get red spots. I can treat myself for lice and run the comb through my hair, but it is a lot of work cleaning the entire house and all my clothes etc.....so I am trying to figure out what to do here. I saw one piece that could have been a nit in my hair, but it also could have been a clump of hair spray from this morning.....any ideas?