Cannabis likes wet/dry cycles, so you shouldn't water until you can poke your finger 1" into the soil and it feels dry. A popular way to test if the plant is dry is to get accustomed to how light or heavy your container feels.
I'm not too experienced, but it's my impression more frequent cycles are better. Like, 2-3 days. If you have to wait 5 days it may indicate your soil doesn't drain well (i.e., not enough perlite). What kind of soil do you use? Maybe using organic nutes makes it ok to have less frequent watering.
Regarding your nutrients, hopefully one of the organic people will answer your question. If your soil doesn't have nutrients in it, waiting 3 weeks to feed is too long.
I'd be careful using SuperThrive. I've read it can cause problems (hermie) when used as a supplement. I use a half-drop (per gal) in my germination soak water and 1/4 tsp/gal when I transplant (photo sensitives. So far I haven't transplanted an auto).
Consider starting a grow journal in this forum with all the details (soil, lighting, temp, humidity, light cycle, ph in and out, tap or filtered water, etc.). Document what you do (feedings, etc.). This will help people help you as your grow continues.