The Burn?!?!?!?!?!

I have been lifting for about 4 months religiously. mon, wed, fri.  I know i am getting stronger because the weight is often getting heavier.
Im training for strength and i do a full body workout , 5 sets 5 reps with the last set to failure. When i complete all sets fully then i up the weight 5 kilo.
 
However I am not feeling the burn as often these days and havent felt it for a few weeks. Also, I don’t wake up the next day achey. Maybe once or twice a fortnight .
 
Is not feeling the burn normal?
In regards to the aching should I just count myself lucky?

simple add more weight. but achein and the burn means your not used to lifting weight.i feel pumped when im finished and a bit tight but no burn achein next 4 me stopped years ago. OR try doing your last few reps SLOWLY with form thats the burn i thin u mean lol try it fing kills 4 a few minutes after lol 

The burn you talk about is DOMS (Delayed Onset Muscle Soreness) and means very little.
 
DOMS usually occur when the muscles do something they are not used to and will reduce as you get fitter and the muscles become accustomed to working. The lack of DOMS does not mean you are not improving.
 
They will occasionally rear their head again, but usually it'll be because you've had a few beers, or a bad nights sleep or some such.

As above really, sounds like your body has gotten used to the exercises and workload you are giving it.
This doesnt mean to say that you wont be getting the same growth stimulus.
Dont base a workouts effectivness on how sore you feel afterwards.
 
What you could do is change your exercise selection around a bit, either just for a session or 2 or cycle your routine abit. ie a few week ( say 6 ) of a certain number of exercises, then change for all new exercises for the next 6 weeks, then back to your first choice and so on...
 
Either that or change your rep range etc, add a couple of high rep sets in and so on.
 
It is gererally a good thing to change your routine around a little every now and again even just the order of how you do things makes a difference.
 
All that said if you are getting stronger as you say, your obviously getting things right . 
As i say try not to base the workout on the soreness etc afterwards just the progression you are making.