What's wrong with my plant?

Could someone help me figure out what's wrong with my plant?
Day 48 from seed. Day 23 of flowering. My plant recently started to show bad signs. Lower leaves are yellowing and finally they go brown and die.
Meanwhile there are some suspicious black spots on upper leaves but they don't seem to go worse.
I've tested my watering ph which is about 6,6.
Because I currently don't have flowering phase nutrients, I've given my plant little amount of veg. fertilizer. I've taken off quite a bit leaves now and I'm starting to think that my plant will die fully soon.
So I would be really glad if someone could give me some suggestions.
PHOTOS: https://imgur.com/a/FN7oP

Looks like it could be potassium deficiency, especially if you've only been giving it veg nutes. Cannabis needs potassium during the flowering stage and there isn't much way to get around that, so try and see if you can find a source for some.

The plant did not have enough N from the light veg feedings. It just used its reserves for the beginning of flower stretch and bud set. I would fed a healthy does of 50/50 veg bloom food.

Stop taking off leaves too you should only do that if they are badly infected with a mold, fungus, leaf miners or something like that. If you have a deficiency then stripping old or discolored leaves will only make it worse. Let her pull all the nutes out she's doing that to fuel new growth always let them fall off on their own.