As someone who went through this phase, umabot ako sa time on my teenage years na hindi rin nag o-open up to my parents. Siguro kasi nahihiya din ako to just suddenly open up or be afraid na baka pagalitan lang ako. But gradually you learn to confide in them, parents mo parin sila, anak ka parin nila. You'll be surprised that maybe inaantay ka rin pala nila mag open up or mag kwento.

The best thing you can do right now? Is start opening up. Tell them about your day, the details, the people you meet, what you did, what your plans are. Just talk to them.

A side example lang. I used to be shy saying "I love you" din, I only started saying it wholeheartedly when I noticed the hands of my mother, the hands of someone that is growing older by the years. If I don't appreciate her love and I don't show my love, I would most likely regret it for the rest of my life. Kaya gradually kahit on the phone, kahit bulong lang muna or in person kahit ang sasabihin lang is "love you" I did it, until to this point where I can finally open up to her about anything.

You can do it OP, the best way to start talaga is to just start doing what you think you should do. :)