You can actually lose your mucus plug like 2-3 months before delivering..
Contractions aren't normal at 33 weeks, but it isn't uncommon..
Im only 31 weeks and I have lost my mucus plug as well. I experience contractions several times a day, but my doc said not to worry until they become persistent.
You can loose your plug up to two weeks before you go into labour, but because your only 33 weeks and experiencing contractions, even though they are irregular I would get yourself down to your hospital asap, because you will need to have steroid shots for the babys lungs if they cant or decide not to stop it, if they find out you are indeed in labour and not strong braxton hicks, good uck