Hair is thinning on the right side of my head, what can I do to help this and what is a likely cause?

Hello and thank you for your question about hair loss at 19 years old. Many factors could be responsible for your hair loss, including genetic factors. To get an accurate diagnosis, schedule an in-person consultation with a hair restoration surgeon in your area. After your diagnosis, an appropriate course of treatment can be prescribed.  Your treatment options may include Minoxidil to help sustain and thicken healthy hairs or PRP (platelet rich plasma) treatments which can also stimulate hair growth using components from your own blood. Your hair restoration surgeon can recommend other treatments after your examination and diagnosis. Good luck! 
- Jacqueline T. Cheng, MD

Hair does tend to thin on the right before it does on the left in most men.  Your story is a bit atypical, though.  When you say your hair was more curly when it grew back in, was this hair that had fallen out and then regrew, or just hair growing back from being trimmed?You may be better off with an in-person consultation.  If your diagnosis is in fact male pattern hair loss, you can then discuss options such as platelet-rich plasma (PRP), minoxidil (Rogaine), finasteride (Propecia) and laser therapy. 

Without a photo and full details of the story, it’s nearly impossible to say. There are dozens of reasons to lose hair. A photo narrows things down considerably.

It would be best for you to be examined by a board certified dermatologist.  Preferably, one who specializes in hair loss.  Hair thinning can have many causes.  It's best to be examined and start treatment early. 

Assuming that you are a male, the most likely cause of thinning is early genetic balding. You might see a doctor and get this confirmed and treated