Are methods of influencing a baby's sex (such as changing one's diet) permissible?

I have 2 daughters Alhamdulillah. Now me and my family expect one baby boy as my next child, so I can search on Internet and found some method can increasing possibilities of baby boy, like, the woman's diet (alkaline food) plan, her period time calculation, male diet plan, position of intercourse (sex), time of intercourse (sex) and moon night calculation. So can I follow this method? Is it permissible in Islam? I know Allah will give me which is better for me, and I will happy with it.