birth control; missed period first month

i started taking Loestrin 24 on June 5- about 5 days into my period, which ended the day after i started the pill. I took it at the same time everyday throughout the month, and had sex on June 27 and have been having intercourse since then (without a condom.) However, i did not get my period in July and i am really worried. Does it occur that you miss your period the first month that you are on the pill? i would be grateful for any insight. thanks!