18 year old male with hair thinning issues.

In general hair loss as you describe it is usually male pattern balding (since you lose hair in a certain pattern).You need an exam and diagnosis to confirm this.  Your doctor can test for vitamin deficiency.

Thinning Hair -- Rogaine, Propecia, Viviscal, Progesterone, PRPIf you have thinning hair you really need an evaluation to see if it is genetic or from another cause like stress or autoimmune. If it is determined to be genetic there are many options and traditional treatments like rogaine foam and propecia pills can be used. I have great success in my practice using injectable progesterone and prp to the scalp. Postmenopausal women also benefit from spironolactone. I suggest seeing a dermatologist with expertise in hair loss. Best, Dr. Emer.

Male pattern hair loss could show its initial signs in early 20s and occasionally as early as 16.  You need to be evaluated by a good hair doctor macro and microscopically.  Looking into your exam and family pattern are the two key points that a doctor can make a good diagnosis.  Following that a treatment plan needs to be formulated for you to prevent further hair loss or to restore your hair if need be.

Certain vitamin deficiencies, including vitamin D, can contribute to hair thinning and hair loss.  If you are deficient in vitamin D, I recommend supplementing this and re-checking your vitamin D level in a couple of months.  Make sure to take your vitamin D with a fatty meal, as it is a fat soluble vitamin.It would also be helpful to have an evaluation with your dermatologist to determine if there are any other appropriate treatments for your hair thinning.  Several factors may be involved including genetics, hormones, other vitamin deficiencies, among others. 

99% of the time this is due to genetic balding. Your biggest enemy is the progressive balding that you might
have in the next 5-10 or so years. The degree of balding (thinning) that you are showing
would suggest that before you undertake a hair transplant or try to find out iv you have a vitamin e problem, you should see a good doctor who will make the diagnosis of genetic balding. He will most probably prescribe the drug
finasteride for one year. Get Bulk Measurements of your hair to determine the
degree of the progression or if you successfully stopped or reversed the hair
loss with this drug you need to get insights into your immediate and long term
future. If you are developing a more advanced balding pattern which the Bulk
Measurements will show over a one year time frame, then you and your doctor
need to develop a MASTER PLAN on what to do.

If, for example you are going to develop a Norwood class 6 and 7 balding
pattern (very advanced), these patterns will develop well before the young men are 30 years old,
you and your doctor must project a worst case scenario before you embark any more aggressive treatment. . The older you are, the easier it is to predict future hair
loss. At 19 years old, it might be difficult if you are not destined to be a
Class 6 or 7 pattern, but in your late 20s, the job of predicting is easier.
If you bet on a horse in the Kentucky Derby, you can never be sure that the
horse will win until the race is over — likewise, your balding should be predicted
and you may be able to predict the final pattern at the age of 26 or possibly
earlier with two measurement of your Bulk Test data one year apart while you
are on the drug finesteride.. Don't jump to a hair transplant too quickly as
you might find out that you might be Class 6 or 7 balding pattern men.