Spotting!! Help - any experiences?

Erin

I'm 5 weeks pregnant, had some bright bleeding on wiping at 4+3 so I went to the doctor - he sent me for blood HCG tests 48 hours apart which were 1100 then 2768 at 4+5, so it more than doubled which is good. But I'm still having bits of brown spotting!!! Why? Anyone have this in their first trimester? Hoping everything will be ok. I have some mild intermittent cramping, breasts are a bit tender, no nausea.