Please give advice on how to know when you have lice?

Itch and lice: Itch in the specific body area and visualizing lice, if in scalp - use a lice comb to check for lice.

Have someone check : Your hair. Lice can itch a lot. Lice may be tan to brown gray ; the size of a sesame seed. Nits are tiny, light to white colored deposits that adhere to hair. Head lice may be on back of head, neck, eye brows or behind ears. They cause pink to red bumps w central dot.