Saggy loose skin under chin...turkey neck? (photo)

Congratulations on your amazing transformation. I would recommend seeing a plastic surgeon in your area for assessment. It is likely that muscle tightening and skin excess removal are in your future, but there are many options for aesthetic improvement to the submental area. Options include lipo, face/neck lift, RF Microneedling with laser work. Good luck to you on your neck aesthetic journey!

Congratulations on the weight loss! The neck can have horizontal wrinkles and wrinkly skin especially after losing weight. Genetics as well as from sun damage and aging can also play a key role and can explain why some people have a worse flabby neck appearance than others who might've also lost the same amount of weight. This area can be very bothersome to patients.
Surgical treatment with possibly a neck lift and short scar facelift is the best way to get rid of them but this will leave scars which some people don’t want.
There are several nonsurgical options to consider. Some can be done at the same time. Surgery combined with Botox and filler injections, laser treatments and chemical peels before or after surgery are all good options.  
These procedures can be done safely in the office and the results are often very satisfying. An in-office private consultation and examination with a board-certified plastic surgeon would be the best way to fully  address your specific concerns and determine the right treatment plan. I would recommend that you see a board-certified plastic surgeon in your area that is a member of both ASPS & ASAPS and performs a lot of facelifts & neck lifts but also offers all the nonsurgical options such as injectables and laser treatments. Go over your concerns with them and make sure above all, you walk out of there with several options and an idea of the pros and cons to each of them as well as realistic expectations. 
I hope this helps. If it does, please take a moment to up vote this answer on the “respond” button on the top right.  Have a wonderful day.

Thank you for your question and pictures.  Congratulation with your weight loss.  You have lost elasticity under your neck, meaning you have loss skin.  This can be removed by a necklift which tightens the skin under the chin giving a more youthful appearance.  This can be achieved under local anaesthetic, which means the downtime associated it a lot less.  At your age you do not want to be bruised for 4-6 weeks.  The incision are just in front and behind the earlobe, running just on the edge of the hairline.  It doesn't go into the hairline as this can cause hair loss.  Please make sure you find a reputable and qualified plastic surgeon who can assess you properly to give you a realistic idea of what outcome you can achieve.  All The Best