Everything I'm about to say is meant in the nicest way, so please keep that in mind.
Four rejections is nothing, not even a drop in the bucket compared to what'll pile up in your inbox if you do this for any length of time. I've gotten dozens of rejections for the same short story, and goodness knows how many more the novel I'm pitching.
Rejection is part of the trade, and you'd better get used to it. You probably won't know why they don't like it, so it's pointless to wonder (but I do sometimes). If anything, rejection should be motivation to try harder and write better. I only published my first short story last year, after spending the preceding three years seriously writing and reading shorts.
Self-publishing won't make anything easier. Take it from me. I spent $1000 to have a fantasy novel printed that was terrible by any reasonable industry standard. It just wasn't good enough, and that's why it didn't sell. Looking back, it was a mistake, a shortcut to nowhere, the illusion of achievement. It's a huge investment, and these companies often do not offer any other services unless you pay for them. You will have absolute control, but also total responsibility for marketing, editing, and making sales happen.
If you give it your all, if you study writing and read a ton of stuff, if you spend time on here asking people questions and, above all else, if you KEEP WRITING, then you have a chance. No promises, but persistence is your greatest asset.
Do. Not. Quit.
Do. Not. Settle.