What Are The Chances Of Pregnancy Through Non Penetrative Sex?

I have been taking Prednisone for 11 days now (decreasing 10 mg every four days) and will be done on the 16th. I am a virgin, but my boyfriend and I were fooling around April 1st and he came on his boxers, I felt a little leak onto my boxers (not much), and I don't think any got on my underwear, or light pad (which I wear for vaginal discharge) And if it did is it possible for sperm to swim through clothes? My last period started March 12, and it should be due this week. I know I'm not pregnant, but I started freaking out that I might be. I've been feeling mini-cramps for a couple of days now nothing like I normally would before my period, but my period refuses to come and I'm usually very regular. I've never been on any medication before, not even birth control, so is it possible for prednisone to delay your period? Or do you think there is a good chance I might be pregnant? I've also been under a lot of stress lately, so could that be the cause of the delay as well? Thanks for any help you can offer.