The best start is to put fat burners aside and focus on the the obvious: your diet and your training... in that order of priority too.
what are you eating everyday on average? How much activity?
only with that we can pinpoint any obvious problems, because in the quest to get leaner almost all the variables have to be perfect. don't be discouraged if it hasn't kicked in yet because there could be some glaring inconsistencies that you haven't seen yet. everyone here will be glad to help.
of course if we can't find the answer then seeing a doctor to check thyroid issues may be necessary, but let's hope that's not the case.