If you missed your expected period (or it is late) you should first take a pregnancy test to confirm or exclude a possible pregnancy. If the test is positive, you are probably pregnant and you should go to your gynecologist for further diagnostic confirmation (ultrasound and blood test). If the test is negative, you are probably not pregnant but you may be experiencing a functionally active ovarian cyst. Hormones produced by functional ovarian cysts cause the period to delay and promote cycle irregularity usually for 2-3 months. You can consult your gynecologist about this.
Stomach pain (pain in the upper abdomen) and vomiting are probably due to a stomach disorder (gastritis for instance), not a genital disorder. You may consult your primary health provider about this problem.