trying to conceive at 42 nearly 43

What shall I do? I have had tests cannot find anything wrong with me I am 42 trying for number 4 baby ..had 3 mc.s the only thing I haven't had tested is progesterone because I have irregular periods is 26-28 days shall I get natural progesterone cream to try and get pregnant it has been over a year since last pregnant any advise welcome thank you.