I'm experiencing headaches which rare because I only had 2 or 3 headaches during this 4months. Also cold feets and cold hands. Any reason as to why this is happening?

Cold feet and cold hands is often a result of low blood pressure. It is common place with me. I am frequently besieged with cold feet and hands. My BP is usually 116/74. This does not push a lot of blood through the extremities.

A solution for some is to increase intake of niacin, especially a good time released niacin.

Head aches are a different matter. Even the experts will not have an answer to the why's and wherefore's of head aches. Just be glad you have not had head aches in a chronic fashion since your concussion. many of us suffer head aches for months after a head impact.

Head aches may be influenced by L-Theanine but my 200 mgs of L-Theanine twice a day has not caused head aches for me.

My blood pressure is currently 106 / 74.
As for the headaches it could be excess taking of l-theanine. If I exceed 200mg I'd get headaches.

Your low BP could be the reason for being cold. I take the L-Theanine twice a day, 200 mgs each time. Many supplements like L-Theanine and L-Tryptophan do best taken in smaller doses multiple times a day.