Please forgive this question, but I'm a new user to WSPR and am scratching my head a little....

I started using WSPR about 24 hours ago and have been running it for about 18 of those hours. I'm using an FT-817 and a G5RV with antenna tuner. I have been posting some great spots from beacons in the US (I'm in the UK) and the Ukraine, so I know that I can hear people. In all that time though, I didn't get a single report of my signal being received by anyone! I'm just wondering why this might be and if I should be turning my attention to something in my station. I know the radio transmits, or at least it does on other bands, as I have made contacts using SSB and with my handheld scanner, I get some 'mush' received when WSPR transmits. So, am I just suffering from the statistics - no one is listening on my frequency, or is there some other systematic error - sound card issue or some such?

Is there a troubleshooting FAQ I've missed somewhere?

Thanks in advance

John