Not sure what kind of stance you use but try using a basic peek a boo stance and keep everything tight. Then practice wiping the jab. All you have to do is turn your rear hand around, try looking it up on youtube. Since your having trouble landing punches dont worry so much about slipping punches right now. Use your nice tight peek a boo stance to block punches, then start trying to counter from blocking your opponents punches. Greys right on about orthadox vs southpaw and vice versa. Make sure you keep your lead foot on the outside of their lead foot.