First off, definitely

! I'm pretty knew myself, but the people here are fantastic and whatever kind of support you need, this is the place to find it. I agree with the others, talk to your doctor to find out your limits, if you hurt yourself the road gets longer. As beerab said though, eating right is a huge step, so even if you can't exercise much, just watching your eating habits can help a lot.
As for feeling worse than normal, you said you've stopped drinking Mt. Dew and eating McDonalds, these are both very addictive substances so your body is going through a detox of them. That is a LOT of caffeine and sugar to cut out all at once. It is definitely great that you've done it, but you have to give your body time to adjust to being without all of it. When I quick soda I found that drinking tea was enough caffeine to et me through the day and I could slowly drink less to get over the addiction of it.
Also, I don't know how much water you drink, but that could help get your body adjust quicker because it help to flush your system. Drinking water has many health benefits!
Good luck on your journey, we are all here for you. Make sure you check out the support group threads, they've got all kinds, including ones for PCOS.