To stop or not to stop drinking soda????

So as a dieter/ person who is changing their lifestyle, I often find it hard to want to give up certain things. For example, my diet wild cherry pepsi. Yes I understand that its not the best choice...and No I consider it a treat for me! Well, I'm starting to wonder if my soda choice is starting to affect my running.  So I busted out my 5 miles last week in epic fashion I must say! Well, I walked into the gym tonight with a tid bit of an ego! Thats right, I was struttin my stuff like a varisty football player!! I was going to get on that treadmill and bust out my miles in less than 35 minutes. WRONG ...DEAD WRONG. Oh my  heck, it was awful. I warmed up for the first quarter mile and then decided to give it a go. Oh my gosh, I felt like I had never run before in my life. Usually my legs will hurt a little until I get really warm and then I'm ok to just keep going. They ached tonight, just ached. My mind was playing tricks on me. It was terrible.... Not to mention my husband just finished up his little run and then sat on the bench and jammed to his pod, while I was gasping for air thinking I still have 2 miles to go and he's finished are you KIDDING me. UGH. Needless to say, I did get my stuff done. I know I should be proud, because I did cut another 2 minutes off of my time...but still It was so stinkin hard!!