Welcome to MS. You will learn a lot here and see that we discuss a wide range of issues including the questions you raise. There are many among us that can identify with you. Two regular contributors that you should watch for are cant_remember and Life's A Dream.
Abuse does not occur in a vacuum, and I would suggest that even if there's no explicitly sexual component (at least none you can remember right now) you may have endured physical and emotional abuses. Those can feel just as crippling.
The sort of hallmark sexual abuse symptom is a distorted sexuality that will manifest itself in two or three ways. First, there are those of us that become hyper sexual and often engage in compulsive, high risk sexual acts. Others of us become close to asexual, completely shutting down our sexuality and living a monk-like existence. The third manifestation of distorted sexuality is an unquenchable thirst for porn and masturbation. Ask yourself if you've engaged or are engaging in any of these behaviors. Your answer could make you more confident in your self-diagnosis as you approach therapy.
Now lets talk shrinks. In general I am no fan of the profession. I personally believe it is largely populated with neurotic hacks who'd be unable to counsel their way out of a paper sack. You've seen a number of therapists that never helped. And I have, too. However tempting, we cannot paint an entire profession as inept, though. A good therapist will develop a trusting and respectful therapeutic relationship and become a watershed of recovery and healing. It can happen for you. They do exist. The good ones are out there and they're worth the drive.
But your therapist will not fall into your lap. A good therapist will be discovered with patient research and through the interview process. You may talk to three, four even five before you find one that you have a rapport with. Or at least one that doesn't give you the creeps. It's much more like dating than a mental health consideration should be. But it is what it is. A decent therapist will do a phone consultation or waive the first session's payment if you do not become a patient. A good therapist will not harshly judge you for asking questions that I think are entirely reasonable. As a matter of fact, get that out right at the start of your first interview. Say, "I'm Bill12 and I'm seeking therapy because I believe that perhaps I was sexually abused in my very early childhood." That'll really get the ball rolling in a hurry. I find if I say the hardest thing to say first, just to get it out, I won't spend the entire time talking around it. You gotta man-up for this...
NO one said healing was easy. It takes courage every day to face these things. But finding that courage is worth it. Finding that therapist to help you sort through these issues is worth it. Why? Because you're worth it. Look at this process as the gift of love that you give to you. You'll do this so you can stop trudging through life as a disconnected spectator. You'll do this to become healthy and happy for the first time ever. It's a nice feeling, trust me.