21 yr old female, hair and weight loss, fatigue, irritated scalp, anxiety, high stress, irregular periods, mood swings, thin spots?

Multiple poss, Whatever the issue, stress may be resulting in or adding to the issue. Alopecea areata is hair loss that can be caused by stress, get on some zantac (ranitidine) 150mg. If no medical reason is found, and often there isn't ( adrenal insufficiency, thyroid, autoimmune dz) then Mirtazapine is a great drug for insomnia, appetite and mood/anxiety. It works well in those with your profile but you need to be seen.
See physician. There could be many medical reasons including thyroid function abnormalities. Please get checked by your primary care physician who will do a battery of blood tests to come to a diagnosis. A depressive disorder with associated anxiety can explain some of the symptoms too.
Multi-symptoms. Any changes in your eating habits?. May need to consult your primary care doc. For full medical workup to rule out medical causes for symptoms.