<human>: I've been running on/off for a year and have a personal best record of 5:30/km pace for 10k. I am now starting my "formal" training for a 21k in February 2016, which gives me about 12 weeks of preparation. I am very hopeful that I can do this. However, I have recently changed shoes because my old very generic Fila training shoes broke down. I bought a new pair of Skechers Go Run Ride 3 because it was cheap and it had good reviews as far as research goes. I have also been researching on tips & techniques on proper running form since I do not know if what I've been doing these past few months is what more experienced runners would consider as correct running form.

But what happened during my first run of using the shoes and trying out to correct my running form led to a horrible decline in my running. I was about 2kms. in and I was attacked by side stitches, and not those mild ones where you can just adjust your breathing and it goes away, no, these were crippling side stitches that hurts more with every step you make. So, I decided to stop running and start walking just to calm down these side stitches, so after 5 mins of brisk walking making sure those pesky side stitches have gone away. So I ran my again, starting slowly this time and keeping my breathing intervals in check, but after 1km or so, they hit again! I also noticed that I was already so tired even only after 3kms at a slower pace.

After that I ran for 30 seconds more and decided to fuck it and stop running since it was hurting so bad and I was really tired.

What did I do wrong? Was I wrong in buying those shoes? Or was I wrong in trying to correct my running form? Or Both? 

Sorry for the wall of text!

Can you summarize the given text in a few sentences?
<bot>: Decided to up my game so I bought new shoes and tried to correct my running form, but my body STRONGLY disagreed.