I just entered tip of penis inside the vagina n just after 7 hours she had periods, she missed next period n feeling weak. is there chance f pregnancy?

Always possible: Anytime there is sexual intercourse (male and female parts together) there is a possibility of pregnancy. Because she had a period right after is reassuring that she is not pregnant but not a surety. Missing a period is a sign of possible conception. Take a pregnancy test and be sure.

There is always: Chance of pregnancy when you have sex without contraception. Only positive pregnancy test or passage of time will tell.