I wouldn't worry about it unless you started bleeding. I didn't even see a sac let alone a baby on my ultrasound at 4 weeks pregnant. At 6 weeks pregnant on the ultrasound I still can't see anything (tech does, I don't). Trying to tell how far along you are with numbers isn't always accurate. I wouldn't go by that. I'm sure you numbers will double and when they do, don't worry about it. 4-5 weeks is really early to see anything! Good Luck!
thats still kinda early to see anything. i think i went at 6 weeks pregnant and only saw a tiny dot. so at 4 almost 5 weeks...idk but your hcg is doubling. that sounds good.