Sore Breasts Before Period, Light Headed, Headache, Nausea. Pregnancy Test Negative. Advise?

I'm 32 periods been normal & on time each month since puberty. Last 2 months I've had very sore breasts specifically around the nipple which I normally only have a week prior to my period.. also my periods changed these last few months w/a stutter start then approx 3 days of what seems normal bleeding, no clots which I used to have often & then its done. At night I use only a super tampon which I couldn't do before, I am a lot lighter at night also in these months.. took a pregnancy test because usually it means I'm pregnant as I've had 3 children but, this time it read negative. It was a cheap test but... still negative. I've also had some light headed spells & headaches around my time of bleeding sometimes even nausea only haven't gotten sick... & the light headed spells, headaches & nausea are not consistent nor constant.. just outta the blue. No hot flashes, or night sweats. Can you help me?