It is entirely possible that you where sexually abused as a child. But please remember that you're memory is hazy for a reason. Its your brains way of protecting itself. I know you want answers but pushing yourself to think about it may do more harm than good. You may want to read this article about why you maybe shouldn't talk about trauma, it really calmed me down reading this for some reason: http://www.new-synapse.com/aps/wordpress/?p=1137
The type of sexual touching that you describe between yourself and your brother, happens often. It is my theory that it happens moreso if there are problems with physical/mental/spiritual abuse in the home. Your story could have been my own dear. The physical abuse that happened in my home i believe had much to do with my being a sex addict starting at the age of 13. I had two boyfriends in high school (only 1 of them knew i was regularly seeing two people). I was searching for something to fill the void of lack of love from my childhood. Just as i became a sexual addict, i also became addicted to substances early on. Neither of my parents ever tried to get me help for the way i was raised, the days i missed from school, because i was up all night living in abuse. I became the worst junkie i knew and yet, not once, ever, did either of my parents do anything but blame me for being a trouble maker (in their lives). After they took from me my childhood, and set me up for a terrible life, they blamed me from the get go, for being a bother to them in their lives after i turned into an adult. Now that i'm older, and wiser, and clean and sober, I realize, the abuse did not stop after i became an adult. Every time i was in the company of my parents and they did not try to talk to me about what happened, to at least apologize.. i realize now that it was just more of the same. In other words honey, you can't make a silk purse out of a sow's ear. You can't expect your mother to do anything but the wrong thing, if she hasn't come to it yet that what she did to you abusing you for all those years needs to be formally addressed with you, by her sincere and heart felt apology and willingness to accept that she did grievous harm to you and in fact, as your mother, owes you to help you overcome the effects of her parenting. There is a thing, called Cause and Effect. I'm so sorry that there is no one taking responsibility for the harm they caused you, that you have not heard the "i'm sorry" that you need to hear, and that you have not had your mom come to you with understanding and want to help you get on your feet after the years of abuse. I believe that you were raised, as i was, by a Psychopath. Someone void of empathy and unable to have any understanding of the harm that they have inflicted on their own defenseless child. My parents never even had the decency to have a death bed confession as to their actions and how they harmed their 4 children (who all had terrible problems starting with young adulthood). If i ever tried to get my mom to talk, she would actually take her fist and beat her own face, saying you want me to take the blame (for how her kids lives all went off track). She was sick. Your mother is sick. Some get well if they have the courage to admit their own limitations.
All you can do is to understand the reality of where you've been and plan on living your best life. Being able to converse with other children that have been raised in dysfunctional homes (like myself) can help you in your life to avoid some of the pitfalls that come from living with abuse. I can help you with that, and it would be my honor, in fact, my whole reason for staying on Medhelp since i joined in 2012 is to help others who grew up in the same type of home that i grew up in.
There's a group called ACOA, or Adult Children of Alcoholics or Dysfunctional Families that meet weekly and are I believe an International Group (stemming from AA). There you can talk to others about what it was like growing up and have a safe place to learn that YOU ARE NOT ALONE.
I'm here for you dear girl, i'm proud of you for reaching out.
It does sound possible. If you are a legal adult now, seek counseling. Tell the therapist that you are concerned because you had an abusive mother and have blocked out your childhood memories. Then what comes up will come up. Go lightly and give yourself a lot of leeway, this was not your fault.