I need some advice on my sexlife. [21/M] in relationship with [18/F]

We have been in a relationship for a year and 3 months now and in the beginning everything was perfect, as time progressed however, we started having sex way less. I know that this is a common thing and all but it has gotten to a point at which we fight about it. I get frustrated whenever she stays over an entire weekend and nothig happens at all. No sex, no blowjob, not even a handjob. The worst part about it is that she seems to think that sex is a punishment for her, she explained to me that she proceeds to think "Oh no its been x days since last time I have to give him sex or he'll be upset" and that turns her off. I have tried giving it time and it was finally starting to get better but now it has gotten to a point where it is too much on me. I started keeping a calendar and since 2016 we have had sex 5x while 3 of those weeks were school vacations and she was with me 24/7. How can I improve her sex drive? How can I bring this up to her without always being the bad guy for complaining about not having enough sex? I really need some help with his, do not let me down Reddit.