I usually have a normal 28 day cycle but after my m/c and D&C I didnt get AF again until 5-6 weeks later. It sounds like your cycle might just be off because of the experience it had went through with the D&C. Sadly pregnancy symptoms are very similar to AF symptoms so it is hard to differ between the two. Sorry about your loss and I hope everything works out for you.
I am sorry for your loss:~( I do know that you are more fertal after having a baby so you could be. But just like having a term baby, your baby takes awhile to regulate and return to normal. After having each of my babies it took an average of 5 weeks for AF to show. So you may not be late but then again to answer your question, yes you can get pregnant right away. You never know what will come first. Ovulation or good old AF. Best of luck!
It is not wise to try to conceive right away your dr is incorrect. I have had a few miscarriages and they say to wait two cycles before trying to conceive again. You have to give your body time to recoop. Your body just went through something tramatic give it time to rest. Sorry to be harsh.