Been going to the gym religiously, have great strength, good cardio, but recently have adjusted my diet to eat cleaner about 4 weeks ago.
I haven't lost any strength (yet) but it doesn't take long to wear out in the gym.
Rep ranges go from 15-10-8-6 and then one more of 15. My muscle groups feel on fire or about to blow up and have almost no strength after each exercise with about 6 exercises per day
My gym time has gone from 2 hours to just over an hour. Is this all mental and I'm psyching myself out? 
"Eat cleaner"? What does that mean exactly, OP?
Did you drastically cut calories? Carbs?
The answer could lie in your dietary change.
Have you always been doing the same rep range and routine?
You said you go religiously...what does your training schedule look like?
When was the last rest/deload period you had?
There are a lot of variables. 
Cleaner means I won't touch processed foods. Fats have been cut down to <70g, proteins are about 200g carbs about 180g per day.
Lifting schedule is Monday, Tuesday, Thursday, Friday and conditioning on Wednesday and Saturday.
De-load is every 6 weeks.
I have several years experience of bodybuilding and powerlifting.
If it matters, I am 6' and 235lbs.
I feel toast after each workout after a shorter time... But I am also working out by myself for the first time in a long time.
Goals dictate the training parameters.
What is your fitness goal?
Pure and simply, you are tired becaue YOU ARE NOT EATING ENOUGH CALORIES.
If your numbers are accurate, you are consuming at most 2150 calories a day.
According to
http://www.calculator.net/calorie-calculator.html?ctype=standard&cage=35&csex=m&cheightfeet=6&cheightinch=0&cpound=235&cheightmeter=&ckg=&cactivity=1.55&printit=0&x=70&y=15
you need over 3000 to stay the same weight.
You are currently eating at a rate to lose 2 lbs of weight a week.
Plain and simple, you are running a high enough caloric deficit that your body has gone into energy conservation mode, and your energy levels have therefore plummeted.
You want your energy levels to go up? Raise your fat levels by another 10-20 grams, and your carbs by another 100 grams a day.
Fats have been cut too.
Theres your answer op