I think you should buy some new soil and start a new seed.
what does the soil pH mean? that soil cant go up from 4.7 and down from 3.7?
PH is measure of acidity or alcalinity. Normal tap water is around/between 7.0 to 8.0 PH (it varies)
Your Soil PH was between 3.7 and 4.3 ... very acidic.
Cannabis likes to grow in soil between 6.0 - 6.5
You can take all of the above statements as Fact.
Here's the reason why a cannabis plant wont grow in your soil.
Nutirent Uptake.
In order for a plant to grow .. it needs to be able to eat.... it only likes eating certain elements (like nitrogen for example) at a certain PH
so the soil has to be in a "Nutrient Uptake Range" so that plant can eat from it.
Here's a confusing chart to show you what i mean about nutirent uptake
(look at the right hand 2 bars ... for soil)
I've got plenty more of these charts
,,, but for now .- you can take it as law that if you keep your soil PH range between 6.0-6.5 ... you'll be doing much better than your current grow.
I'll find you some pictures of decent store bought soil for growing cannabis in

(i'll come back and edit them in)
(my old soil)
TaNgs current soil
Mr Ganjamotos soil
Cheap "home depot style" soil (last choice for me) - need to mix with perlite to get it light. (cannabis loves light and airy soil)