Everytime the American market opens, my portfolio goes red

I live 6 hours ahead of American time and my Portfolio is always doing great before the American market opens (which is 3:30 PM for me).
As soon as it's 3:30, every stock drops into the negative.
Why? Im sorry If this is a stupid question. Im quite new to stocks, but I just don't understand why this happens with EVERY stock? Are you guys mass selling as soon as the market opens? (By the way, this did not only happen the last few days, it's every day. Sometimes more, sometimes less).
Thank you for any answers.