What to do?

My cat has had trouble with bowel movements, and recurring constipation, along with the vomiting of undigested foods. Could it be "Megacolon" disorder? One of my cats throws up undigested food a lot. When he comes out of the litter box he rubs his bumb on the rug, I took him to the vet and the vet took out a dried up piece of poop. That cant be fun or comfortable. For the last two days I have been giving him petrolium jelly but i dont want to do more harm. My dad recommended olive oil. What about flaxseed oil? I am looking for a naturapathic cure/remedy and safe cat dosage. He will be 5 yrs old in April.
Thank you for your help in advance!