my 1st pregnancy and its a lil weird?

[Chicklet]

so i recently fount out that i was pregnant and i had my 1st ob appointment and the doctor said that he didnt see any thing, i had a blood test done that confirmed the pregnancy but my ob says that if i am im only 4 weeks well that cant be right my soon to be husband is in the navy and has been out to sea sence the beginning of august we last had intercourse in july, the end of it, so that would make me at least 6 weeks right? well im a lil confused he sent me over to have blood work taken could there be something wrong? any help? i feel as though im the only one, i kno im not but it seems lik it