My dog acts like he’s bipolar! I don’t know what to do!

[Livey2220]

I have a male prapso Shih Tzu and dachsund mix, he is almost 4 years old. His father is a prapso Shih Tzu and his mother is a Shih Tzu and dachsund mix.
When Benji was a puppy he acted like a normal pup, but once he was about a year old he became aggressive towards his father and they had to be separated. There is now no other males in my home, just his mother who is fixed. I do know aggression with males is normal behavior for male dogs who have not been fixed, but his behavior doesn’t stop there.
One moment Benji wants to be cuddled and pet, he’s loving and a sweetheart and then it’s like a switch goes off and in a millisecond while you’re petting him he snaps at you and bites. He will begin growling and start aggressively barking when he’s on your lap and in your face and then attacks your hands. All of this for no reason, when he comes to us for attention.
It is impossible to put a collar, harness, muzzle, etc. on him sometimes and other times he’s fine with it.
He’s not aggressive towards other dogs in public or people. In fact he loves being approached and pet on, he seems so sweet! But when he is picked up by someone he gets aggressive and tries to attack the hands. He does this more with people who he is frequently around, not strangers.
The best way to describe him is it seems he has major mood swings and anxiety. He often hides under the couch, sometimes just to bark aggressively and growl as if he’s about to attack, he does this especially to my female if she gets too close. He’s also very protective of whoever is in bed.
He will cuddle my female and play with her everyday and then sometimes he’s aggressive and shows dominance with her, but they have only had a few altercations over the years.
I truly do not know what is wrong. I have thought maybe a hormonal imbalance is causing the mood swings. They are very intense and I never know if he’s going to be good and loving or bad.