HCG LEVEL

Hi mommas! My last period started May 8th. I took a pregnancy test on Monday and it was negative. I took another test yesterday (first response gold digital) and it quickly popped up with a Yes+. I called my OB and he did a blood test and my HCG level is 17. I am reading online that is extremely low, but I'm barely even 3 weeks pregnant and my doctor said implantation happened probably a day or so ago. However, I am worried. Is this a normal HCG for this soon? He doesn't want to see me until I'm 7 weeks (June 26th).