First of all don't worry hun, sometimes it takes a while to conceive a little miracle but it will happen eventually. I know the pain of losing a child at 12 weeks too but never give up because there is hope!
Since you've lost a child before I would consider checking yourself with a doctor for any reason why you can't however lots of women have managed to conceive after a miscarriage and if there's nothing stopping you here's a few handy tips :)
Weight - If you're a little overweight, to lose a few pounds can really help improve your chances of conception.
Diet - Try to ensure you eat plenty of fruit and veg as the vitamins and nutrients in them can help you to receive beneficial nutrients in your body.
Vitamins - Taking a multi vitamin tablet can easily help you receive everything your body needs to up your chances of conception however there is better brand called pregnacare conception tablets for him and her that can seriously up your chances, they have been known to help many a couples conceive within the first month of taking them.
Timing!!! - After your period I would stock up on ovulation prediction kits because these can be your key to help you get the perfect time for conception! Once you find out when your ovulating you need to have sex at that time as this can help your chances of getting pregnant in a heart beat.
And last of all..
Sex - You need to ensure you have regular sex. If you can have sex around 2-3 times a week it's all you need as sperm can survive at least 3 days in your body meaning that on the days your having a break, your partners sperm can rebuild to be stronger and the sperm already inside can still have a tiny chance of getting you pregnant.
If you join all these together you should conceive in no time!
,May all the luck be with you and may you be blessed with a baby soon.
You should see a doctor. Had you had a follow up after your Miscarrage?