After 1 fresh cycle and 2 FET cycles that have failed what are the next steps to be followed to determine the causes?

Speak to the RE. Meet with your re to review all treatments to date so he/she can break it down into components and see why you haven't conceived and what your options are for success. Since most of my patients conceive on their first ivf cycle, and you've failed multiple cycles, you should strongly consider gathering up your records and seeking a second opinion!