Why has my dog had a hard time pooping for several months

It is probably due to your dogs anal glands. When the glands become too full they can become impacted and even possibly burst. When this occurs your pet loses the natural lubrication provided by the glands and therefore can not use the bathroom like he normally would. If you see him scooting him butt across the floor it is a key sign of gland problems. But do not dismiss this advice if you havent seen him scooting!! Some dogs just do not know how to express their glands themselves and have to have a qualified professional do it every few weeks for them.

I recommend you take your dog to a local groomer or a petsmart or petco- they will be able to check the glands for you and express the anal glands externally if needed. They will also let you know if they feel impacted or were unable to express and then u will be advised to take your pet to a vet as soon as possible. I suggest AS SOON AS POSSIBLE! A groomer will just charge you 5-10 dollars to do it for you but if you wait until they are too full a vet will charge you an arm and a leg!!!

Also have you changed your dogs diet recently or are you feeding him a grocery store dog food??? If so check the ingredients if it is mainly corn filled it can constipate your pet.

And lastly, either have a vet check him for worms or buy an over the counter dewormer from a pet store and give it to him. If your pet has worms they could be the reason why it appears difficult to use the bathroom.