Trinh,
I am so sorry to hear about the loss of your precious little man Timothy.
I lost my baby boy Noah due to abnormalities of his urinary tract and kidneys at 20w5d in Feb 2006. We were "advised" to wait around 6 months to give me time to "heal". I knew I wanted another baby. We waited 1 cycle and decided to try on the 2nd cycle. We were unsuccessful and decided not to try on the 3rd cycle as that would give me a due date in Feb 2007 which would be too close to Noah's birth date. After not using protection the one time during the 3rd cycle, we found out I was pregnant. We now have a healthy, beautiful 18 month old little man named Harrison.
The only advice I can give you is to do what feels right for you. If you want to start trying again asap, then that is your choice.
From my understanding, they medical profession likes you to wait until you get a regular cycle before you start TTC. That way you have a LMP to go by... though from my experience, most Dr's like a dating scan done anyway.
Wishing you all the very best sweetie. I hope you get the BFP you're wanting when you're ready and go on to hold another beautiful baby in your belly that you will take home with you. Big hugs
Lisa