I started taking the pill 1+ yr ago for menstural control. Why am I still having severe mood swings only every few months around the end of the month?

You need more. The pill is quite helpful for pmdd (moodiness around your period) but it may not completely fix it. You should talk to your doctor about your symptoms. An ssri like Prozac (fluoxetine) could be helpful but you need tone checked out to make sure nothing else is going on.
Try Yaz (drospirenone and ethinyl estradiol) pill. Yaz (drospirenone and ethinyl estradiol) is low dose birth control pill that also improves pms.
Pms. Premenstrual mood disorder and premenstrual physical symptoms are somewhat different. Not all birthcontrol is alike. The birth control Yaz (drospirenone and ethinyl estradiol) has been marketed for mood symptoms. Ssris also work for menstrual related mood problems in some women.
Mood swings. It is most likely due to the ocp. Maybe an alternate with lower concentrations of the estrogen, progesterone, or testosterone (if included) would help. Consulting with your md would clarify why and provide options. If the ocp was prescribe for mood swings consider more traditional treatments for mood swings including mood stabilizers, antidepressants, and/or psychotherapy. Exercise regimen?