Surely you must realize that checking the low side pressure is not telling you much. (I'm assuming you used one of those crappy "recharge" kits that includes a cheap low-side gauge. Those things are useless at best, damaging at worst if they contain sealer and you put any into your AC system.)

At a minimum you need a full manifold gauge set to do any kind of meaningful diagnostics. As @Doc says, if you've never worked on automotive AC before it's probably best to take to an AC technician. There is no magic bottle that's going to fix your air conditioning by having you "fill it to the green".

Please do yourself a big solid and take it to an auto ac specialist.  Trying to fix this extremely complex system yourself is a recipe for an expensive disaster.