For how many months can Plan B affect your cycle?

Plan B is a huge dose of artificial hormone, which can effect some women's cycles for months. Many find it just causes a delay of their period for a week or two, or sometimes none, but I know of many who have waited months to get a regular monthly cycle back again. It's a lot for your body to deal with.

For future reference, if you have an emergency like a condom split, try to take the emergency contraception asap, as it has more chance of being effective the sooner you take it after sex. If you had been relying on Plan B completely this time, you might have found it unable to help, leaving it until 72 hours after sex, because of where you were in your menstrual cycle. You were possibly in your fertile window already, if you have a short cycle. This could have meant getting caught out & therefore possibly pregnant.
This doesn't sound likely in your current situation, as you used a condom.

If you ever have a condom accident when you're likely v close to ovulation, then I suggest the other emergency pill called Ella, as it's the only emergency contraceptive pill proven to work in the 24 hours leading up to ovulation. For Plan B it may well be too late.
You can checkout the Ella website to see that.