Well as for your ovulation date you really can not tell EXACTLY that you have ovulated UNLESS it is seen on an ultrasound and or you got pregnant - all the other things such as ovulation testing and the discharge you see are all 'indications' of ovulation but they are NOT exact.
As for your cycle being 20 days - You should check your thyroid - as everything else is normal - but if not your thyroid - then more than likely it is due to anxiety - as this can vary your cycle.
Your blood being thin - this could be bleeding from the fallopian tubes
or ovaries that is draining into the uterus and out of the uterus - you will need an ultrasound to tell for sure.
As for your cycle - well a cycle is normal if still within 2 to 8 days of bleeding - so that is normal.
If nothing on day 3 - perhaps there was a blood clot
blocking the cervical outlet - hard to say without doing an exam on you.
And, I think this all comes down to you having Anxiety and Endometriosis - and hence when you want to get pregnant you should work closely with an ob/gyn - because although tests can be normal - there are other indications here that you might be experiencing infertility problems due to a thyroid condition, endometriosis or Anxiety (although you might not think much of it, it does play a very large role in this).
Also a menstrual cycle is normal when it is anywhere from 24 to 35 in length with bleeding anywhere from 2 to 8 days.
I hope this helps
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