It sounds like an almost identical situation that you posted about in September last year, where you had unprotected sex and were worried you might be pregnant?
Do you think it might be a good idea to get yourself on the pill or have a contraceptive device (like a Mirena coil or hormone implant) put in, since you have now been put at risk of unplanned pregnancy twice in 5 months?<img title="Undecided" src="include/wysiwyg/tinymce/jscripts/tiny_mce/plugins/emotions/img/smiley-undecided.gif" alt="Undecided" border="0" />
Are you not able to take the morning after pill?
I can't help answer your question, but I am concerned that you have put yourself at risk so soon after the last time, especially considering how much distress it caused you then.
Please go to see your doctor and arrange for a pregnancy test and also some STD tests to be on the safe side (I'd hate you to have got an untreated STD when your immune system is already seriously supressed from being on post-transplant meds).