It's possible you might have been pregnant, but had a Chemical pregnancy. It would explain the sharp pains and heavy bleeding. It's extremely unlikely you would be pregnant now with both of those. It's also possible it's heavy and painful because it was late. You could see your doctor if you choose.
It's best you went to see the doctor, there could be a few things which could have gone wrong.
1) Hormonal imbalance, this makes you have most of the symptoms of being pregnant. This could have also caused the delay with your period
2) You could have been pregnant. Sometimes you could be pregnant but it doesn't show on the HPT, until a few weeks later.
3) The sharp pains you are feeling could be because your period was late, if they are unbearable, pls see your practitioner, maybe even get a scan done, this would show whatever is happening in your uterus.
All the best.. :)