Oh I so understand! It is such a heart break. I'm currently in the 2ww, and dreading the possible let down, again. ((((rasjane)))) I would tell your mil so you don't have to experience comments like that again, no matter how well intentioned.
Everyone is different, but it seems like if you have a doctor you trust it couldn't hurt to get a few tests. Or maybe call and see what they think. I ttc'd for 9 months, then had a miscarriage. At that point my doctor started doing all the hormone tests, ect. Part of that is because I'm almost 39 and part because I'd tried for awhile before my loss.
Hang in there.