You dont use fertilizer? Apply some Nitrogen and Phosphorus
3-5 months since popping from soil? It looks weak and thin, again add Nitrogen (especially) and some Phosphorus
You must repot the plant in bigger container and when i say big i mean BIG (repoting is huge stress)
BUT dont repot at this point because you will stress the plant so much that you might stunt its growth permanently, its already stressed enough its fighting for its life.
Since you were already shading you plant (with the curtain) You either remove the curtain so it gets more light or you place it on a window with more DIRECT sunlight throughout the day and when it recovers place it in a spot were it hopefully gets all day direct sunlight. (Do it gradually)
The insects i guess are crawling on top of soil which if i have to guess is peatmoss based, this is very common when using peatmoss based soil ESPECIALLY indoors, a lot of houseplants have them. You can buy and place mulch.
I dont recommend a grow lamp. Why? Because if you are not carefull you with mess up the plant cycles (photoperiods) that happens very easily.
What i recommend you do is: If you use peatmoss based soil (with little to no nutrients) you can get some organic N-P-K fertilizer higher on the N. Buy a organic root stimulator and after 1 month if plant recover repot it in BIG pot. Dont under/over water just enough, i say leave it now to dry a bit (so oxygen goes to the roots) and then give it a small dose of n-p-k fertilizer with root stimulator (dont use root stimulator a lot since plant is in small pot just once a week). Place in sunny area.