Why could my skin itch even though I don't see any rashes or bite marks?

Itch. There are many causes of itch without a rash. Systemic causes include kidney failure, liver failure causing elevated levels of bile, blood disorders such as leukemia, lymphoma and iron deficiency. Thyroid disorders and diabetes also can cause itching. The most common cause however is dry skin and using a good moisturizing cream such as cetaphil or cerave and anti itch lotion like sarna can help.
Symptom. Itching is sign that the nerve fibers in the skin are irritated. There are a number of reasons for itching including an allergic reaction or even an irritation ofvthecskin. You can be allergic to a drug which can cause itching but it does not do enough to cause redness. There is damage from the outside or inside causing these symptoms.