Please help!

I am in desperate need of advice. I started knitting my Slytherin scarf two days ago. I decided I wanted to make it in garter stitch. I started out perfectly fine with no problems. Once I got up to five rows it was impossible to continue because the yarn had tightened itself to the point where getting the needles in to make a stitch was an act that required divine intervention. So I ripped it all out and started over. I knitted 3 rows and the same thing happened again. So I ripped it out and started over. 6 rows. same problem. Ripped it out. 2 rows. Same problem. Ripped it out. each time I’m discovering that new stitches are appearing that weren’t there before because the yarn was separating. So I cut the yarn off at a fresh bit and started over again only to have the same results that I’ve been getting for the past two days.
What have I been doing wrong?? I’ve followed Amy’s video instructions to the letter.
Why am I having so much trouble getting started?
How can I keep the stitches from splitting and tightening up on me?

You may be knitting on the tips of the needles. Be sure to form the stitches on the full barrel of the needle. It could also be a very tight tension in general.
Some yarns have a tendency to split and you just have to watch each stitch to make sure you’re not creating new ones. Count sts after each row to check. It may also be that your yarn became a little frayed and split because you were ripping out and re-knitting it several times.