Thanks for query.
As you say your period are not regular,chances of pregnancy
are also uncertain because your ovulation time is not fixed.
Pregnancy test sometime be false negative,but may be you are pregnant.
May be meftal spas
cause contraction and may be that white material is early sign of pregnancy.
but don't worry,whatever happened is happen,go to some gynae,get USG done.
Took treatment for your irregular periods
Everything will be fine.