so when i get to a point when I can't figure out what it is I start from scratch and think about my every move with my seedlings. 

i tend to over water/love mine. i know it was me because my underwear had my name on it.

so start with reading directions on your soil or lacking soil fertigation solution. good place to start. 

clean everything. twice. hands too.

because I overwater i have a new love/hate for water/moisture bourne trouble.

learn to correct your bad habits barring that, grow within your limitations. I learned that perlite is a friend of mine.

see where this is going? start over slowly and pay attention. is it drafty? too warm, too cool? things you miss are going to kill it off. light intense enough? I use 20w at 6-10 inches, softest growth. they get water until it gets a second leaf min. then just enough to maintain moisture i would argue against any run off at this point, not until you have some roots but it isn't a very long period or shouldn't be.some would say until run off this works too. it is important just to not over or underwater it. and give it a close intense soft light.

and it isn't so much the brand of soil if it's good soil and you can control the moisture and have a handle on the nutrition when it needs. but a good soil saves a lot of worry when you know how it works for you.

Anyways, stick with it see if you can get someones bag seeds to grow that way it lowers your learning costs a bit. Good luck !