Of course your doctor may have reasons for asking you to wait so long, but you have a good question.
For both my miscarriages, they said I should wait for one normal period, then I could start trying again the next cycle. One miscarriage was 9 weeks and one was 17 weeks, but the same advice for both.
With my 9-week miscarriage, they did more blood tests to make sure the HCG levels were decreasing at the proper rate before they gave me the "go ahead" to start trying again. They wanted to be sure it wasn't a molar pregnancy. (Look it up online.) If it had been molar, I would have been forced to wait a year. Basically, they fear you have a rare condition (cancer maybe?) if your HCG levels aren't dropping or start increasing after a miscarriage. The doctor said if I got pregnant in that year I would not be "allowed" to carry the baby because they wouldn't be able to tell the baby apart from the disease or condition. At least, that is how I remember the story.
Based solely on my experience, that may be a reason to make sure all is normal before starting again. Chances are, everything is normal and miscarriage was just a fluke that happens to most women.
I'd recommend calling your doctor and explaining your feelings, and asking if you could take a blood test.