If the frames do not fit, they do not fit. It can take some time and back and forthing to get them right but they should not charge you. Make sure you have them on the way they are meant to be worn (mine slip down my nose some; that will give you headaches too, if the "angle" they are on your face isn't correct) and I would try them a few days, see if they do give you headaches and if there are ways to help that.

I'm too lazy to take my glasses off (used for reading only) so wear them on top of my head or down my nose and look over the top, etc. and that's not fair to whether they hurt or not/cause headaches.

Usually my headaches are caused by the angle of the glasses (carrying mine around not in a case and wearing them on top of my head causes the frames to become uneven so, again, the angle is not correct), the too tightness should tell you you have been wearing them too long and need a break from them?

No, they should not put grooves in the side of your head or give you headaches but you have to wear them properly too, not constantly, or take shortcuts caring for them; they're expensive instruments! You put your phone or computer in a case of some sort to protect them when you carry them around (my computer cost $49, my carrying case might have been more expensive, I don't remember :-) and I should take my own advice and treat my $600 glasses (two pairs, one for upstairs by my bed and one for downstairs here at my computer) better!