Try something like this.
I had a full course load, and although I was both a volunteer for the IRS Volunteer Income Tax Assistance Program and a private math tutor, I still maintained a high grade point average.
I maintained a high grade point average with a full course load, despite dedicated time as a volunteer with the IRS Volunteer Income Tax Assistance Program and as a private math tutor.
or something that combines these ideas.
Note that it's A private math tutor, not "an." There is no vowel sound.