What do I do?

I'm not sure what to do, my 3 1/2 month old throws up soo much he's not gaining weight. I was breastfeeding him but I decided to try pump and bottle feeding to see if it would help, it didn't. So I tried it with rice cereal still throws up, tried formula still doesn't help finally tired formula with rice cereal and it's helped the most so far but I want to breastfed idk what to do :( breastfeeding was so easy with my others anything else I can try