i have ectopic pregnancy last jan/2011 and lost my left uterus,right now im 5 weeks pregnant but im in danger of having a miscarriage,is having 1 uterus the reason? or having ectopic pregnancy weakened my chances of conceiving?

Well, some folks are born with 'twin pipes' - two vaginas, two cervices, and two uteri.  But I'd imagine this would be a part of her post if she had this.

Ectopic pregnancy can be caused by a number of things - wonky fallopian tubes with folds that 'catch' the egg, uterine fibroids/cysts, an IUD, etc.  If you've got fibroids or something going on in there, you should get that cleared up before trying a pregnancy.  Otherwise, losing one ovary/fallopian tube shouldn't be an issue at all - that's not the baby's 'house,' and you have another set :)  Definitely find out what your doc is talking about when he/she says you're in danger of a miscarriage.  Good luck!