December 8th I had unprotected sex & on December 9th I took the depo shot as a substitutuion of the day after pill. Can I be pregnant. I get nausea and diaherra & migrains.

It's too early to be able to tell if you are pregnant or not.

No, the depo shot should not be used as a replacement for the morning after pill. Depo stops you from ovulating, it does not terminate pregnancy.

This is a question of emergency contraceptive methods.
If yo have taken the morning after pill it prevent pregnancy (>99% success rate). Nausea is probably due to the pill than pregnancy in this case.
To get nasea in pregnancy it takes 6 to 8 weeks from your last periods.

Depo shot may cause irregular bleeding with other side effects,

this is a question of emergency contraceptive methods.
if yo have taken the morning after pill it prevent pregnancy (>99% success rate). nausea is probably due to the pill than pregnancy in this case.
to get nasea in pregnancy it takes 6 to 8 weeks from your last periods.

depo shot may cause irregular bleeding with other side effects,

Please re-read the OP's post. She didn't take the morning after pill, she took Depo as a substitute for the morning after pill.

Also, where are you getting your info on nausea in pregnancy? Where are you getting the 6-8 week time line? It's not accurate. Every woman is different. Some feel nausea before they even miss a period. Some never feel nausea at all. Some will be fine for the first trimester and then suddenly suffer through nausea for the second and third.

I'd really like to know where you're getting these numbers from.

Sorry I just understand that you have taken depo shot only. Deop shot is not an alternative of morning after pill. As I mentioned morning after pill is >99% effective if taken within 24 hrs,
Intra uterine contraceptive device (IUCD) can be used as an emergency contraceptive methods if used within 5 days of unprotected sex.

Yes, some do not feel nausea at all but the one gets nausea due to pregnancy, is around 6 week (due to increase of HCG level) this is the average figure, in this case there is no way to get nausea after 4 days of unprotected sex. I pointed out that.

True, after 4 days it wouldn't be possible to feel nausea due to pregnancy, but I still don't agree that the earliest is at the 6 week mark.

With my daughter I started having morning sickness at around the 3 week mark, before I found out I was pregnant. Nausea can be one of the first symptoms of pregnancy, even before a missed period.