it sounds like you are doing everything you can. what you have to understand is that no one is going to gain 20 lbs of muscle in 6 wks. what you've gained is going to be mostly fluid at this point. you may have a few lbs muscle and a few lbs fat, but for the most part, this gain is water. over the first 3- 6 weeks, your body has filled with more water, which is totally normal for this type of cycle. at some point in the cycle, that fluid retention is going to level off, which it sounds like has happened. the gains you make now will be more "real". just keep eating and trianing hard. over the rest of the cycle, you may gain a few more lbs, but i wouldnt expect another 20 lbs. you have created a super hydrated anabolic environment. you are probably stronger in the gym, allowing you to work harder and tear more fiber down in each training session. your recovery will be better and over a 3 month cycle, speeding up the muscle building process. weight gain comes on easy and fast on AAS. muscle gain takes time and lots of work. if you can keep 10 lbs of solid muscle at the end of this cycle, once the fluid goes down, you are doing pretty damn good.
btw, 20 lbs is a huge amount of water to hold. too much IMO. i would consider using a low dose of an AI to control estrogen from the test. also, keep an eye on your BP. you dont want to be walking around with elevated BP for months. even if it is minor, over time, it can tax your kidney function. if you are above normal, the AI will help get you back in check.