I appreciate that you are still trying to learn marketing and not sitting back on your laurels or outsourcing the work. There shouldn't be any upper bounds on your growth just because you make more than one person needs, assuming you are one person at all.
Even if you might not need this skill now, you might still need it in the next project. Also you are the best possible person to understand what works and doesn't work and why as you will have the indepth understanding of the product.
That said, I do not have much to offer in the way of advice. I hope someone else would be able to.
In the meanwhile, I would like to pose some questions and maybe you can figure it out yourself or someone can help you.
1. As someone else have pointed out, have you been iterating on your work? Even ads need lots of iteration, feedback and course correction before it clicks. The same goes for other marketing channels too. Here analytics and googling can be your friend.
2. All the channels you have been speaking about take time to produce rewards. They are more like a garden that needs sowing, tending and weeding before results start to appear. How long have you been doing these activities? Have you been giving consistent attention to each channel overtime?
3. You have the most important treasure key to marketing success. Customers. Have you been talking to your most ardent customers? How did they find you? What value do you add, in their own words? What problems have you solved for them? What capabilities have you enabled by solving the problem? Where do they hang out? How can you reach more of these people? It is very important that you be able to talk to them and see your product from their viewpoint. I would recommend that you record the interviews (with your users' permission) and playback often to get a good understanding from their perspective. Maybe you are targeting the wrong market?
And an obligatory recommendation to "Obviously Awesome" by April Dunford. It is a short book but full of interesting insights.