Mid 30s. periods have become less heavy/slightly shorter last few months. dr says all ok/still fertile as long as periods are regular/on time. true?

Probably, but ...: Small changes in your periods are not too concerning. Female fertility declines with age at different speeds in different women. If you're trying to conceive without success for 6 months in your mid-30's, see a rei specialist to check your ovarian reserve or 'egg supply' (egg numbers and quality) with fsh, estradiol, and amh blood tests and an ultrasound scan of your ovaries.