Does masturbation cause hair loss? I'm 19 and I think I'm suffering from hair loss.

Masturbation does not cause hair loss.The most likely cause for your loss is Androgenetic Alopecia-male pattern baldness.This is due to genetics and hormones.There are several adjuncts that are effective at stopping hair loss.These include Finasteride ,Minoxidil ,Low Level Laser Light and/or PRP (Platelet Rich Plasma). I would recommend consulting with a Dermatologist or experienced Hair Restoration surgeon.

No , masturbation does not cause hair loss. The reason of the hair loss may related with factors other than genetic like connective tissue disorders, stress, anemia, lupus, medications, hormonal and seasonal changes, nutritional problems, severe diets, bulimia, protein/calorie deficiency, zinc and essential amino-acid deficiency, mal-absorption (intestinal and digestive problems), A-vitamin excess, general anesthesia, affective mood disorders.
Drugs that may cause hair loss in woman 
Anti-coagulants such as warfarin and heparin  Epilepsy drugs, especially dilantinGout drugs, allopurinol and colchicumAntihypertensive drugs, diuretics, beta blockers.... etcSo you may need dermatoscopy and ıf needed a skin biopsy and to have a full exam with an hair surgeon and/or endocrinologist , to find out any reason for hair loss. 

The number of grafts depends upon the size of the recipient area you want to treat, the thickness of your hair shafts and the donor density of available hair. A good doctor knows how to assess this so see one.