Need fitness advice! ASAP!

I'm seventeen nearly eighteen, about 5'4" and around 105 lbs. I've never had issues with my weight or body until recently. I've somehow managed to land the quarterback, and we've been dating for a while. Just as my pathetic life was looking up - A week ago - I noticed cellulite on my upper thighs, and that just one side of my bum is saggy. I have no idea what to do, I've never worked out before in my life, and now I'm freaking out. I know I can do squats, but I can't afford a gym membership, and due to back problems I can't engage in any activity that will strain my back. I have two months to tone up before I have to see my boyfriend, and I need to fix the issue because right now my ass looks like my fifty year old mothers. HELP!

Also, would you recommend running? Any possible exercises or anything really, because this is bothering me so, so, so much! Thanks.
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Thanks a million, you guys. Great advice from all of you. (:
Need fitness advice! ASAP!
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