Good afternoon Shahidul, and thanks for the question and pictures.  

It's not uncommon for young laurels to struggle their first year.  They use most of there energy trying to get roots established and take hold in their new location.  This does make them more susceptible to pests and diseases.  

In your case, it looks like you are dealing with some form of leaf spot, or perhaps a blight.  Your pictures look like leaf spot, but your verbal description sounds more like a form of blight.

Typically neither one is fatal to your plants and both can be controlled through good housekeeping; pruning affected leaves, keeping the surrounding area free of debris.  There are also chemical solutions for more advanced cases.  Here's an excellent article:  https://portal.ct.gov/-/media/CAES/DOCUMENTS/Publications/Fact_Sheets/Plant_Pathology_and_Ecology/COMMONPROBLEMSOFMOUNTAINLAUREL031111pdf.pdf?la=en

Having said that, it's difficult to accurately diagnose leaf spot problems without actual physical samples to test.  I recommend sending samples in to the Penn State Plant Clinic for testing.  It's an excellent service and is totally free to all Pennsylvania residents.
This is their webpage.  It includes any directions you'll need as well as recommendations and contact information.

https://plantpath.psu.edu/about/facilities/plant-disease-clinic

Good luck Shahidul!  

Good morning again, Shahidul.  

Thanks for the additional pictures.  The quality is great and I'm very glad you sent them.  
The leaf damage I'm seeing is typical of the adult black vine weevil.  Laurels and rhododendrons are two of it's preferred hosts.
https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/black-vine-weevil/#overview

The black vine weevil is a small (1/4 - 1/2 in,), flightless, dark beetle with a pronounced snout.  They are strictly nocturnal and are almost never seen during the day.  It's getting late in the season so they may no longer be feeding, but if they are, going out after dark with a flashlight should expose them.  You can just pick them off or knock them into a jar of soapy water.   

Here's the thing.  While damage from the adult BVW is generally only cosmetic, their larvae can be devastating to your plants.  Initially feeding on smaller more tender roots, they soon progress to larger and larger roots even attacking the bark.  An adult weevil feeds for two to four weeks before dropping down and laying eggs.  A female (and they are all females) can lay from 200 to 800 eggs.  

Since you've been seeing this problem for awhile, I suspect that by now you are dealing with a pretty heavy infestation of larvae and that's what is causing the dieback of your new leaves and growth.

The organic solution is to introduce nematodes which will feed on the larvae.  It's a slow process and you might have to do this a couple times before you get a large enough population to have an affect.

Alternatively, you can look at a chemical solution. A soil drench around the roots using a product containing Imidacloprid is your best  solution.  This is a systemic pesticide, so it will remain effective in your plant's system for a period of time.  depending on how long that is, see the label, you may need a second application in the spring.

https://content.ces.ncsu.edu/black-vine-weevil

This is the same product that has been used for control of the Spotted Lantern Fly.  As with all pesticides, use strictly in accordance to the instructions on the label.
Another option is to call in a Certified Arborist and have them do the work.  There is typically no charge for the initial consultation and you can then decide how you want to proceed.  You can find an ISA Certified Arborist here:  https://www.treesaregood.org/
Just plug in your zip code.

Thanks again for the follow-up pictures Shahidul.  They were a big help.  Good luck with your laurels!