I am feeling comfortable talking to my brother. Could I have been sexually abused in the past a child and I can't remember it, what to do?

Be careful. If you are being cared for by a therapist, professional or lay, competent or not, and that therapist is focusing on trying to get you to remember "forgotten sexual abuse", then please get a second opinion. You may be under the care of a gravely misguided individual who can do enormous harm to you and those you love.
Absolutely possible. It is not unusual for past traumatic events to be "blocked" from your memory. It sounds like you have some suspicions. Speaking with trusted family members would be a good start. Then start regular counseling sessions. Bringing up the past may bring up painful memories as you go through counseling, but untreated abuse can result in chronic anxiety, chronic pain and other physical illness!