My daughter 2 years constantly itches her head but no dendruff or eczema, changed several shampoos. What can it be?

Head lice? ringworm? Itchy scalp can mean many things, including treatable causes, such as head lice (pediculosis capitis) or ringworm (tinea capitis. I would start by bringing your daughter to see her doctor, who may find a treatable cause, or may recommend therapeutic shampoos for conditions such as seborrheic dermatitis, or creams for eczema.
Unsure. Usually, i see this kind of problem in much older people, and often can't find a cause. One simple thing to try is a 1% Hydrocortisone liquid that's rubbed in up to twice a day. One brand i know of is scalpicin maximum strength. I wouldn't try the regular scalpicin which contains salicylic acid - i'd be afraid it would make the itch worse. Any chance there could be head lice?