After 35 yrs the quality of the ovum is poor to get a fruitful pregnancy
. That is first point that goes against the idea of third child.
Now since you are not menstruating I doubt the hormones are not influencing the changes inthe Uterine endometrium. Since the anatomy is well seen with MRI
and nothing was found abnormal, It is time to meet a reproductive endocrinologist
/ Infertilty specialist and get spot on diagnosis.
The earlier you see the doctor and the early the treatment , whatever the the bleak chances will still remain viable for pregnancy.