I had a hysterectomy in 4 months ago, and I am tired all the time. Is this usual?

No. Other issues may be causing fatigue such as mild depression, thryoid problems or lack of estrogen. See your gynecologist for further evaluation.
Maybe. One of the main complaints after any surgery is difficulty with energy returning to normal. Surgery is stressful to the body and it takes time for one to get back to "normal" sometimes. However, 4 months is pretty far out from surgery to feel this way so it might be a good idea to see your doctor and have an evaluation and labs checked.