Milk production with BFN

TTC baby #2 for 3 months. 3 days ago I got a BFN. The next night I felt the urge to relieve the pressure in my left breast and I was able to squeeze a good amount of colostrum out. That breast is much larger and tender compared to my right. I did get a small amount out of the right, but not much. I took another test today and still BFN. I haven't breastfed in 4 years. I'm very confused. Could I be getting a false negative, and if so, is it possible to even be producing milk this early?