Happiness lies in rememberence of Allah (سبحانه وتعالى) and His blessings. It keeps you happy.
One guy performed Hajj (pilgrimage to Mecca) once, and complained about the crush of the crowd. But would you be happy if you were the only Muslim there? No way. You’d hate it. So remember the blessings even when Allah (سبحانه وتعالى) tests you with difficult tests.
Tip: When you say Al-Hamdullilah, mean it. Think about a specific blessing Allah blessed you with. InshaAllah you will increase in your thankfullness and happiness.
References
Muhammad Alshareef. Lecture. AlMaghrib. Breach of Covenant. University of Toronto, Toronto. May 2005.