I had unprotected sex the first night of my period, is there a high possibility of me being pregnant/what is the likelihood that i might be pregnant?

Minimal: Minimal risk for pregnancy under these conditions.

That really depends: Timing is an issue regarding conceiving. On average women in their 20's have about a 20 to 25% chance of getting pregnant each month.

See below: If you had sex within the last 72 hours, take Plan B. Pregnancy is know to have occurred from sex on any and all days of the cycle. If you miss your period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex if you have sex. Get HPV vaccine.