Go over to the entrepreneurship forum and post this same question and you will get the answers from the business owner point of view. That is where most of the small business owners on this forum hang out.
As one of them, I'd tell you there is nothing wrong with you. You can sense you are not being paid fair value. You can sense the owners are offering you more responsibility for a few extra pennies. They are treating you like a pet monkey and asking you to dance more and higher for a couple peanuts. I get it. That is not fun.
Here is the thing, your bosses have every incentive to get as much as they can from you for as little as possible. This is just a fact and it is how they perceive you. You can't get upset about it. You must simply acknowledge it as a fact.
Once you have processed that, go ask for more money. I'd ask for a percentage of savings/profits. Whatever makes sense for your business. But, as a rule, asking for a percentage is a serious signal you understand the business, how much it is worth and your value within the business. People with an "owner mentality" ask for splits, percentages and other stuff like that. Employees (who get paid less) ask for a few thousand dollars owners are happy to pay as long as they are still grossly underpaid for their value.
When you do that, they won't see you as an employee (or dancing monkey, to continue the theme). They will see you as a potential partner, competitor, "up and comer" or whatever. You might not get what you ask for. Maybe you will only get a "good raise" in normal employee terms. However, you will get substantially more than they are ever going to offer you. One important part - you must be mentally ready to leave if you can't make a deal but not emotionally attached to leaving or staying.
This will be your first experience being "in-business." The better you get at these deals, the more money you will be paid in your life. This is how you earn more: YOU ASK FOR IT.