I had a day 3 transfer, and on 8dp3dt, which would be equivalent to 6dp5dt, I only saw the very faintest, nearly invisible line on an earlypregnancytests.com strip. Same on day 9. It wasn't till 10 and 11dp3dt that the line became strong enough not to be imaginary (but still faint). And those tests supposedly detect levels as low as 20. And I am carrying twins, so my betas were pretty high when they did the blood test on day 15.
What I'm saying is, don't give up hope, because day 6 is early to test even for a day 5 transfer.
I don't really remember symptoms, I don't think I had any besides slightly sore boobs (from the trigger shot already, and then probably from the progesterone). That PMS feeling is also normal during that time. Good luck to you!