Delayed Sleep Phase Disorder. Means.

Since the age of 16-17 I have had severe problems maintaining a normal sleep cycle. No matter what, it always shifts late into the night and early morning and my daily commitments suffer as a result. I have never looked into it in detail before because I was afraid, and still am, that I am just looking for an excuse. All forms of sleep hygiene help either just a little or not at all. Unless it is during my 'natural' sleep hours during the morning, the quality of my sleep is also poor and I do not get more than 4-5 times a day on average. I will then sometimes sleep up to 12-14 hours once a week and the cycle continues. I have tried 3mg melatonin a few years ago but I do not recall it being too effective. It is possible 3mg is too big a dosage but I'm not sure. My inability to sleep on time has caused severe personal issues for me as my family insists that I am simply lazy and do not put the effort into sleeping. I don't understand what this means. Thank you.