Am I just parinoid?

I have four boys 2 age 7, 1 age 5, and 1 2 year old? My one 7 year old is always extremely aggresive like he is mad about something. Like he hates life. He is obbsessed with he penis and seeing his brothers or anyone elses "private parts". I know that that is probably just curiosity at this age. I just found him in his room " making out" with a toy while he was basically humping it.I have felt for a couple years now in my mothering gut that he is beening sexually abused. I talk to him about it and explain good touch and bad touch but he always tells me that nothing is happening. Sometimes I can just see it in his eyes he carries the wait of the world in there. He always is so depressed absolutely nothing makes him happy. Should I have him seen or am I just being parinoid because I myself had abuse in my childhood? thank you so much!!!!

Maybe he has not been sexually abused but is depressed because he has got so many brothers taking his parents interest and love away from him.