Do you get headaches near the back of your head? Do you have visible marks or indents on the tops of your shoulders once you take off your bra?
Now, I won't go into proper fitting of a bra, but I will tell you, if it's too tight on your upper trapezius (between neck and shoulder) this could create a trigger point and be a contributing factor to your headaches.
Try this: wear a wider strapped bra, or a sports bra with overall better support. The wider band will help disperse weight along your upper trapezius, causing less of a pain point. And to my ladies that are 'extra' blessed here, I encourage you to try on a FRONT zip (or snap) up bra; no man can provide the level of comfort that a front zip sports bra can.
It also wouldn't hurt to go in for a bra fitting. Unless you've managed to remain the same shape and size during your adult life, you may want to take another look at your sizing.
I hope this quick tip helps!
As always, stay hydrated, stay active!