Constipated for 2 months! (TMI) to

Tiffany • William Dalas born September 18,2016.💙👶🏼 Teen Mom. 💕 YouTube: Dalas’ Mommy
Just some information... My son is 5 months old. He was breastfeed till 1 1/2 months old. Switched to Gerber good start gentle at 1 1/2 months old. Switched to Gerber Soy at 3 months. Now he is on Gerber Soothe. 
Okay, whenever I switched my son to the soy formula, he got constipated fast! When I say fast I mean like 2 days fast. The doctor recommended the soy because of a milk protein allergy. He constantly threw up, had diarrhea constantly, and was upset all the time. When we switched, he was still kind of fussy but didn't throw up as much and didn't have any diarrhea. It switched to constipation and fussy from trying to push so hard. In the past 2 months, I've tried every single thing you could think of. Prune and apple juice. Bicycle and even holding his legs for him. Rubbing his stomach. Warm and cold baths. Suppositories. The list goes on and on. The suppository just made me go and he was still constipated. The prune and apple juice did the same. Everything just makes him go but still constipated. I am so sick of going into the er and the doctors office because they tell me the same damn thing OVER AND OVER!!! Does anyone know or have a suggestion of what could be wrong with my baby? His poop is sometimes as long as my fist and is as hard as a rock. I hold him sometimes whenever he poops because he just scream! The new formula doesn't help and I'm scared to even think about switching to another. Does anyone have any suggestions?