Re-entry to Canada

From the government of Canada's website

Time spent living in Canada

When you are a permanent resident, you can live outside of Canada, but must live in Canada for at least two years in a five-year period. If you live outside of Canada for longer, you may lose your permanent resident status.

For more information on how long you have to live in Canada, see Appendix A: Residency obligation of the PR card application package.

From Appendix A: Residency obligation:

Minimum residency obligation

You must meet the residency obligation to get a PR Card.

If you have been a permanent resident for five (5) years or more

• you must have been physically present in Canada for a minimum of 730 days within the past five (5) years.

If you have been a permanent resident for less than five (5) years

• you must show that you will be able to meet the minimum of 730 days of physical presence in Canada within five (5) years of the date you
  became a permanent resident.

It looks like you have spent too much time living outside Canada and could get your permanent residency removed. I'd contact your local Canadian Embassy or Consulate.

Note that the validity of your PR card has nothing to do with the PR status and the PR residency obligation (RO) that you have to meet which states that you have to live in Canada for a total of 2 years within a five year period to maintain PR. Your PR card will expire every 5 years irrespective of whether you have lived in Canada forever as PR.

You should basically look up the calendar and count the number of days (years) you have physically lived in Canada. If you have lived there less than 2 years between Sep 2013-2018 (assuming you became a PR in Sept 2013) then you have failed to meet the RO and will lose your PR status the next time you try to enter or apply for immigration papers when they check your RO status.

Based on your description, even if you fly out today to Canada you will possibly not meet the 2-year RO till Sep 2018.