Trying again!

Hello all I'm new to this and need some advice. I have lupus and have been trying to get pregnant for 1 year or so. I finally got the green light from doctors and found out I was pregnant and 5 weeks along. Then ended up having an ectopic pregnancy and eventually had a miscarriage . My hcg level is almost down to 0, so my question is does anyone know how long after can you start trying to conceive again??