Renewing Green Card while waiting for citizenship

[Lotus2019]

Hello! I applied for naturalization in late August 2017. I have inquired about the status of my case in December 2018 and was notified that it was placed on a processing hold while the background investigation is being completed. I sent another inquiry about the case on March 25, 2019; the confirmation indicated I will receive a reply by April 16 (which is today), and I heard nothing. My parents went through their citizenship process a while ago and it took them over two years (2 years and 3 months) to receive citizenship, so I don't know whether I should be overly concerned and whether there are any additional steps I need to take. I don't know what's holding up the background investigation as I've been nothing but law-abiding my entire life.
My Green Card is expiring in October 2020. My question is: a) Should I (and can I) take any steps to speed up my citizenship process and b) Should I apply for a renewal of my Green Card while I am waiting? Thank you in advance!

[newacct]

You can contact your Congressman if it's way over normal processing times; otherwise, there is nothing to do but wait.

You don't need to renew your green card. You should be able to get an I-551 stamp since you have N-400 pending.

[Lotus2019]

Thank you for your response! I suspected that I just have to wait. I don't have a Congressperson as I live in DC.
Is the I-551 stamp something that I get in my passport? When do I need to get it and how do I go about obtaining it? I still have over a year until my Green Card expires.

[Enub4]

Thank you for your response! I suspected that I just have to wait. I don't have a Congressperson as I live in DC.
Is the I-551 stamp something that I get in my passport? When do I need to get it and how do I go about obtaining it? I still have over a year until my Green Card expires.

Yes, I-551 stamp is for your passport. You get that once your GC expire and you need to travel abroad (they will let you in with that), don't travel without one and expired GC.