Hey there - a speech pathologist can help identify why you're having the problem you are with your speech.For example: is your tongue not moving cause it's swollen or is there swelling near the nerves that controls your tongue and that's the reason it's not moving well or is there poor sensation (hard to move something you can't feel well) or is your tongue weaker now than it was after your surgery because of limited movement while you were having radiation?
Best to see a speech pathologist to assess your issue and treat it - there are special exercises and techniques that you can learn to improve your speech.

Lymphedma massage may be beneficial too - there are massage therapists and physical therapists that have special certification in intra-oral massage (inside your mouth - sounds weird but that IS where a good part of your scar tissue is!)

Good luck - some things do get better with time but when it comes to speech and swallow - something so vital to our quality of life, it is important to get professional help from the apporpriate therapists/healthcare providers.

Best wishes in your ongoing recovery!