Iron deficiency: can cause restless leg syndrome making sleep difficult. Can be checked with a blood test, and cured with iron supplements. This is what was keeping my daughter from sleeping.
Sleep apnea: not just for old fat men. Under diagnosed and exceedingly common. Can be diagnosed with a sleep study and "cured" with a CPAP machine. This is what was keeping me from sleeping. Most doctors are really ignorant about it. My mother and my father in law both audibly stop breathing in their sleep and snore loudly, but both their doctors told them they couldnt have apnea. In my mother's case, it's because she was "too cheerful".
Not saying you have either of these things, but physiological causes are often missed by doctors, especially PCPs, whose only job I can see is to collect copays and inconvenience people. Rule them out because it's easy to do, and if either is a factor, folk remedies won't do shit.