I am a support main. I have not seen you play, but I just looked at your match history and one of the largest issues is your runes and masteries as well as item build. You seem to have a descent skill order but you go into games with a disadvantage with that setup.
Runes: Try |Magic pen Reds| Armor Yellows| Ability Power Blues| Ability Power Quints|
Masteries: Cunning Tree: Wanderer -> Secret Stah -> Meditation -> Bandit -> Intelligence -> Windspeakers Blessing
Resolve Tree: Recovery -> Tough Skin -> Runic Armor -> Insight
This setup will increase your heals on both yourself and allies as well as giving bonus armor on the heal. Increases cdr cap to 45% and will just simply allow you to get the most out of Sona.
Sums:
and
or
Start with

Then build the following

boots:
or
For the rest of the items they are situational after your core ones.
Try sona with this setup. She is not a difficult champion to play and I believe she is a good place to start as she doesn"t have any skill shots other than her Ult. Try to use her ult offensively to engage on the enemy with your team. Flashing in to hit a 3+ person ult with your team there can easily win a team fight. Its usually her one job in a fight, if you die after getting a good Ult off with follow up from your team then you did your job. You can also do surprisingly descent sustained damage in prolonged team fights as your cool downs are short. At the same time you buff and heal your team slightly with each spells aura.