Hi
I went through that as well. The main thing to note is understanding what happiness is first. We should stop asking ourselves why am i unhappy on sad days. Instead we should ask ourselves why we should be happy on sad days. Asking yourself why will just open the doors to the how
Things that are out of your control will always be out of your control. However, you can control the way you react to such things that are out of your control. For example, if you start getting angry because someone start teasing you (Something that happen to me many times) you can choose to react calmly and not take their insults into heart. However, you can also choose to react drastically which will cause you to flare up.
On a side note, if you want to remain happy on all days, i wrote a post on happiness. In this post, i share 3 daily tips that i use daily to stay happy. You can read the full post at
http://innerpill.com/2015/08/29/why-sho ... -be-happy/