There is no such defined investigation protocol for infertility. Even if everything is normal you may take a month to a year to conceive.As you are 31, you can opt for basic investigations such as usg pelvis,
CBC, BLOOD
SUGAR LEVELS, ft3 ft4
TSH, blood group, Urine r and m etc.
Hysterosalpigogram is an XRay of uterus cavity and fallopian tubes. It is done on 6to 10th day of period. You can do it in this or next cycle as it will guide you for further treatment.