If you've been at 2.5mg day for three weeks straight, and ur still functioning somewhat normal, then I would guess that your estrogen levels were through the roof when you started, and that the headaches are the calm before the storm. Like Oak said, unless you've got a decent case of gyno kicking, I'll bet that ur getting pretty close to crashing your levels. If you start experiencing horrific night sweats, insomnia, terrible aching or sharp pain in joints, irritability, and MFCWW (My Fucking Cock Won't Work), then you better dial down chief! Estrogen crash is not fun. Good luck!