As mentioned above, deficiencies in B vitamins and zinc (common when taking the OCP) can contribute to hair loss, as can low iron. Low iron is a common scenario for women of reproductive age due to the loss of blood each month at menstruation and often a low dietary intake. Women aged 15 years and over need to be getting 15-18 mg of iron per day, which is harder to get from your daily diet than you may think (100 grams of beef mince contains only around 2.7 mg of iron!) If your iron stores (ferritin levels) start to run low, only consuming the recommended daily amount is not going to top up your stores, so you will be forever running at a deficit.
Zinc is necessary for hair growth and to prevent hair shedding and again it is common for women to be getting less zinc from their diet than they need. Australian soil is low in zinc and therefore the plant foods that should be rich sources of dietary zinc are not, meaning we often cannot rely on diet alone to get adequate intake.
B vitamins, especially biotin, are essential for healthy hair, skin and nails as well as a healthy nervous system. The body requires higher levels of B vitamins when under stress, to keep the nervous system supported, so we commonly see low B vitamin status in those who experience stress, especially chronic stress and depletion (see paragraph below).
I recommend working with a practitioner to investigate what your iron, zinc and B vitamin levels look like, and supplementing with the correct dose AND form of these nutrients. Self- prescribing is not recommended so please get in touch.