My daughter will be 4months Dec 19.
Had intercourse in Sept.
Had a period mid Oct.
No period since then.
Sex in Nov & Dec.
Negative pregnancy tests.
Nausea, dizziness & fatigue.
Am I pregnant.
Please give me some advice!

Possible, but could be off cycles still due to your daughter's birth. Are you breastfeeding? That can cause a delay in periods.

When are you due for a period in December? Wait until that time, see what happens... if no period, try another test or see your doctor who will likely order a blood test done.