first, go to EACH employer for the past 4 years and ask them for another copy of the W-2; they should be able to do that for you. Do you have any other forms of income other than that employment?
Then, it may be better to get someone to help you fill out all the back years. Go to the AARP.com website
https://www.aarp.org/money/taxes/aarp_taxaide/?intcmp=FTR-LINKS-INFO-TAXAIDE-EHWERE
and see if there is a site near where you live that can help fill all this out for you. IT IS FREE and you do NOT have to be an AARP member nor do you have to be a 'senior citizen' to take advantage of this.
Note that you had three years to complete your taxes. for the 2015 tax year, you had until April 15, 2019 to file, so is 'too late' What that means is if you owe money, you still owe the money, so you have to file, but if you are owed a refund, the IRS will not give it to you. for 2016, you have until April 15, 2020 to file and get any refund due to you.
good luck!
