My eyebrows and hair have thinned significantly. I changed birth control pills 8 months ago. My thyroid is normal. (photos)

please see a hair expert who is a board certified dermatologist and treats this area frequently.  Best, Dr. Emer.

You cannot diagnosis why you have thin eyebrows with a photo. The old fashion way of seeing a doctor for an exam is still the best option.  

Losing hair on the lateral (outside) aspects of they eyebrows can be very common.  This pattern of eyebrow hair loss can be corrected surgically.  However, it would be important for you to visit with an expert in hair and eyebrows to continue your medical workup.  There are several medical conditions which also cause this type of eyebrow hair loss and they must be ruled out first.  Birth control pills can sometimes cause hair loss, particularly those with progesterone.  Continue off of the birth control for now and seek medical care to determine if there are any other causes of this.  

It is best to see a dermatologist or a hair loss specialist to find the cause for you hair loss. Once the cause is established the proper treatment options can be recommended.

This is something that requires a doctor to evaluate. Women lose hair from a variety of causes, including birth control pills as you already found out. The work-up is extensive, not something that can be done over the internet and requires a doctor who knows about female hairloss.