Yes, I've had the same problem and here's how I solved it: I quit discretionary trading and opted for automated trading.
I've been trading for over 12 years. For the first 10 years, the experience you described wasn't the case with me, because I almost always lost, for several reasons: wrong broker, wrong instruments, wrong strategy.
After solving those problems, I still didn't become profitable, and, for the past 2 years, I've been exactly in the situation you describe: I'd win for 2 straight weeks or so, and then, in two days, lose everything I had made and more. I guess because of wrong money management, but also, after a while, I'd start screwing up on the strategy itself, because I can't keep my impulses under control, and because, if the strategy is discretionary, it is not defined clearly and univocally enough to resist any trading urges. I double up on losers because I get mad and irrational. I stop waiting for the right opportunity, either because I am mad for having lost money and want to make it back quickly, or too confident and excited for having succeeded. In discretionary trading, there's when to enter, when to exit, and how much to bet. Those are the three things you consistently have to do correctly in order to succeed, but "correctly" doesn't mean "successfully": you don't win every time just because you're doing things rationally. Well, for self-control problems which I couldn't solve, I cannot even do those three things rationally. And I am not saying I can trade rationally for 2 weeks and then stop. I can trade rationally for maybe a couple of days at the most, then start pushing my luck more and more and sooner or later I blow out my account. And it's pointless to keep on trying, after over 12 years. So I quit and now I just focus on automated trading, which is so much easier. Actually I sometimes wonder why I didn't quit sooner, when I am so much better at automated trading. The reason is that I was taught to do things that challenged me, and this seemed like a challenge I could conquer. But I was wrong, I couldn't fix my mind, and it now makes sense to quit my efforts to learn to trade discretionary, because the point of this is to make money and not to challenge oneself.
With discretionary trading I have not had a single profitable month within the 12 years I have been trading. With automated trading, it tends to be the contrary, because there's no impulses to worry about, the strategy is a good one because it's been back-tested and forward-tested. Everything seems to be perfect. It really makes you wonder why isn't everyone doing it. Partly because it seems too easy, and so some people don't even try it because they think it's an illusion. But mostly I think it's because it requires a lot of work, and most of those who try it, stop before doing what's required. I don't even know if I've done what's required because I haven't made any money with it yet (actually I have made it but then lost it with discretionary trading). Certainly for me it's much easier to make money with automated trading than discretionary trading.