Why is the truth so important?

Truth is not important because your truth may not be my truth.Think about it. We are creating our life with our thoughts,emotions and actions.How you feel makes your life great or sad.How you act like a creator or like a victim makes you feel great or sad.The only one truth that is important for everyone is " you are creator of your life" so you creating your truths.There are no truths that you must care on. Only yours.

Why did God give me more pain in my life?

Because you believe that there is something outside you that dictate your life.You are creator of your life. You can choose moments, thoughts,emotions and with this you can create what you love or dont love.But you guys just pointing finger on goverments,gods, or something outside of you.

What are the best ways to know if you have bad karma?

There can exist karma or dont exist karma depends on if you wanna see karma in your life.There is no energy that judge you. No karma, no god. You are creator of your life. So only you can punish yourself. How? By thinking about things you dont want. So in the long term they will appear and that is what people call " karma". But its created by creators that observing this reality.

My mind is always looking for reason to worry, why and what can I do for that?

You are master of your mind. So its not " your mind" But its you. That happens when you overthinking. Try meditation. Close your eyes lay down or sit down up to you and focus on your breath. Do it everyday 5-20 min. Also you can try this when you focus on worry, focus on something that makes you happy.