I am a little confused what you mean when you say 3 - 4 weeks pregnant? Do your mean your last period was 3 - 4 weeks ago, or that you ovulated 3 - 4 weeks ago?

If you ovulated 3 weeks ago you would be about 5 or 6 weeks pregnant, and a miscarriage at this stage would be like a heavy period (usually, assuming that everything happens naturally). If your last period was 3 - 4 weeks ago then I suspect a miscarriage would be like a normal period.

Rest up, and I hope you get some firm answers soon

T
xx