My fiance has a 2GB cap and I have unlimited, she went over one month and I couldn't figure out how cause I didn't think I used that much and I stream Pandora/R

My fiance has a 2GB cap and I have unlimited, she went over one month and I couldn't figure out how cause I didn't think I used that much and I stream Pandora/Rhapsody/Sirius on my phone quite often. I finally checked my usage statement and was shocked to see I average 2.5 to 3.5GB. I think my max was over 6GB one month due to streaming Netflix for a few hours.