"What i really need to know is whether it can cause any problems with my periods later on"
it may effect your next period as discussed by worriedbabe but will not have any impact beyond that.
"does it have too much of side-effects? "
There are various side effects with Plan B - cramping, nausea, vomiting, diarrhea are the most common. Not everyone experiences side effects though.
Also, just so you know Plan B is about 75% effective at preventing pregnancy. if taken within 72h of unprotected sex.
Great answer by worriedbabe...
withdrawing and plan b aren't the best methods of contraception. you need a back up, condoms, the pill, the coil or something. that said you need to take plan b AS SOON AFTER SEX AS POSSIBLE. it becomes less effective the more time that elapses between sex and taking the pill. once implantation has occured, the pill will do nothing to prevent a pregnancy. Plan b can make your next period 5 days early or late and has some side effects that are listed in the booklet that comes with the pill.