If you want to learn about market trading, a Series 7 will do absolutely nothing to help you become a better trader. It may, for example, help you identify the pros and cons of corporate debt securities vs. zero-coupon bonds as a long-term investment. If you think this will help your day trading, then by all means... If, on the other hand, you want to become a prop trader or work as a sales rep for a brokerage firm, then you will need the Series 7.
If you want to learn about trading, read as many books on the subject as you can. Authors I'd recommend are Tharp, Douglas, Elder, Schwager. Then watch and observe the market and come to your own conclusions. No offense, but if you are a newbie and you've doubled your account in just a few months, you are experiencing beginner's luck. The markets have been in bull mode since March. Don't mistake a bull market for genius. Learn to trade on the short side to increase your versatility.