Try the prune juice diluted. I gave Camden 2oz a day. It helped some, but not enough. After a consierably miserable amount of time, I insisted he be sent to a specialist. He had been having this problem since birth and no one wanted to take me seriously like I was a hystrionic mother.
I took him to the WVU hospital and apparently he had initially torn his rectum at some point causing extreme pain. He developed a fistula thanks to this (I think it sounds worse than it is, it is a tearing scar more or less). But basically because it hurt so much, he put off pooping, making his bowels larger and harder so that by the time he went again, he tore himself again.
The specialist put him on Miralax (it is available OTC now).
He started out pretty strong, 2tsp a day, he was about a year old. It took a year to move him off of it EFFECTIVELY. Alot of people balk at a child being on a laxative that long, but each child is a seperate case all together and the problem with his regular Dr. was that he wouldn't put him on a lax for very long.
According to the specialist Camden had been cycling through this for so long, that he literally needed to relearn his bowel habits. Over time, I weened him from the 2 tsp to 1.5, to 1 to .5 to .5 every other day, and then .5 after he had eaten foods that may have bound him up some.
He now is on NOTHING and is maintaing a healthy pooping attitude.
If the prune juice doesn't help, try the Miralax. It is easy on the stomach/intestines and it IS NOT ABSORBED into the body. It is all eliminated with the poop. Since your baby is 2.5 mo. I would only give a .5 tsp to start with. It can mixed with anything, it has no flavoring.