You can't do much to stop it, your hairs natural cycle slows down while pregnant and basically restarts when you aren't so all this hair you would have lost but just at different stages now is coming out which is why it feels like soo much. Caffine shampoos are great for helping promote faster growth though. You can technically just put coffee in your hair rather then spending the money but it will slightly dye you hair.
I heard that the hair loss in most women is inevitable. But have been using Nutrafol PP for three months now. Would definitely recommend it. I am 7months PP. I see betterment in hair texture and also a lot if baby hair growing back.