Had mirena out for almost a yr?

I had my mirena taken out in august of last year and I'm having trouble getting preggo Ive been trying for 11 months tomorrow and had all negative results does anyone know what could be the problem I already have 2 girls ages 4 and almost 3yrs old this month any advice would be great. U already asked my dr and he said to keep trying at it but I haven't been trying just waiting patiently for it to just happen. Oh and I started my period on june25,2011-july1,2011 I haven't o'ed yet would anyone know when I ovulate yhis month