How long should I wait for my first ultrasound? I am in my third month now. :)

Normally gynae will perform ultrasound scan either through transvaginal scan (if less than 6 weeks pregnancy) or transabdominal scan to detect your sac and baby's heartbeat. Since you are already in 3rd month, you can request scan from your gynae. The official scans such as NT scan will be around 3rd month too.