That's likely the problem - you underpitched.
It doesn't take much to get started - you don't need a stir plate and flask; you can get started with a simple sanitized glass jar of some sort. Prep the starter with some DME, add it to the sanitized jar with your yeast, cover the top with some sanitized foil, and give it a swirl every now and then over a couple of days.
So if I want to make a starter, can I use regular table suger instead of DME. I don't really have any DME laying around. All the DME I had, got brewed so I would need a substitute.
I have mason jars that I can sanitize and use for a starter, but since I don't have any DME, could I use a cup of sugar and a little yeast nutrient? If I can do that, any recommendations on the amounts of sugar and nutrient?