If hair is falling out in just one place, then it is much less likely that it is related to an underlying medical problem like iron deficiency or thyroid problems. However, it is good that you have had those things checked recently.
One possibility is simply mechanical. As we age our hair gets more brittle, and if you tend to lay on that side of your head exclusively or if you have been combing vigorously there you may notice hair loss
. Sometimes, we also nervously pull at our hair in one particular spot which can cause a similar patch of hair loss.
If this is not the case, then the next most likely possibility would be alopecia areata, which is an autoimmune disease, fortunately otherwise mild, which causes patches of hair loss. If you think this might be going on, then you should see your dermatologist
to rule out scarring, infection or other secondary causes of local hair loss before proceeding to the diagnosis of alopecia areata. The treatment of alopecia areata can include medications to promote hair growth or injections of steroids into the bald patch to halt the process which is leading to the hair loss.
Talk to your dermatologist!