Maternity Leave

Hi mommies. Regarding sa maternity leave medyo naguguluhan po kasi ako, I’m 23 weeks pregnant and currently working in a private company as a project employee. Nakapag pass naman na po ako ng Mat 1 sakanila and they already notify SSS. As per our HR po kasi pwede kong ma avail yung maternity leave as early as 11 weeks before my due date pero need nila ng certificate from my ob. Need po ba talaga magpass ng certificate from my ob? Kasi si OB ko ayaw po magbigay ng certificate kasi hindi naman daw necessary yun kapag nag aapply for that. Thank you in advance po sa mga sasagot.