My partner and I have been trying for 3 months and I was wondering how long after ovulation should you wait to do a test?

The rule of thumb is to test when you miss your period, thus the advertisements for "early dectection" and say you can test 3 days before your period.
As soon as a fertilized egg implants in the uterus, your body starts producing more Hcg which is what is dectected on a pregnancy test.

Most store bought pregnancy tests detect HCG at 40mIU/hCG.

I have ones I bought online that detect at 20mIU/hCG.

J9 has a table that will tell you what your levels of HCG should be at week by week, if you are pregnant.
I have scanned her posts but haven't been able to find it for you, but she will answer :)

It is best to wait until the missed period as MM suggested... Here is the table of hCG

Less than 1 week pregnant = 5-50
2 weeks = 50 - 500
3 weeks 100 - 10,000
4 weeks 1,000 - 30,000
5 weeks 3,500 - 115,000
6 - 8 weeks 12,000 - 270,000
12 weeks 15,000 - 220,000