If God is infinitely merciful, why is there suffering in the world?

That's a big question but in short: There has never been anyone, even the greatest of righteous people, who have an easy life. Wealth has challenges as does poverty, etc. etc. The world was not created to be easy, as many children mistakenly think, but rather complex and the challenges are here to help us grow. Life is full of challenges, and it is up to us to use all of them to grow, to destine our fate. That’s why chazal teach us to bless Hashem for (what seems to us to be) good, as well as for (what seems to us to be) bad (Brachot 33b), because it’s really all for the good, even when it hurts. Additionally, experience clearly proves that people who have undergone hardships are clearly more considerate and thoughtful people. Challenges also help us pray. Prayer is in place of the korbanot (sacrifices), which is from the word “karov”, for us to feel close to Him, which is one of the greatest levels and feelings that anyone can achieve. The closest we can understand about G-d, is like a parent who educates His child, through love and giving, but also through sometimes saying “No” or "Not now", and sometimes guiding us towards and through challenges that seem to be hard, but it’s all in our best interest. That’s part of His being perfect. In short, appreciate the good that He gives you, because many people don’t, and mistakenly focus on the “half-empty” cup. Thank G-d that you feel that direct connection with Him, for that is one of the main goals in life. More so, if you can use your positive and appreciative attitude, as well as your appreciation for the power and benefit of tfila (prayer), in order to help others overcome their challenges, you would really be “karov” and G-dly.