Hcg levels

I recently found out I am pregnant however I'm worried to death because of all the information I was given while I wad in the ER. I had terrible cramping that would come and go so I went in to get checked out. Doctors informed me that my hcg levels were not compatible with my lmp or my vaginal ultrasound. My level was 551. Does anyone know how many weeks that would put me at? My lmp was July 29th should be six weeks however doctor said ultrasound shows a gestational sac but they couldn't tell me how many weeks baby was measuring. I'm so worried!!! I just suffered a miscarriage in February I can't live through another I'm just not strong enough 😢😢😢