Yoga is great for developing positive thinking, and developing confidence. Yoga teaches you to watch your own thoughts. The messages you send yourself subconsciously are very potent. However diet also plays a role. Healthy food is essential and fruit is important for happiness!
I'm not sure about your recent dream. It's obvious that something is troubling you, but I don't know how to interpret it. There are a lot of others on this forum who might have insight.