What Is The Treatment For Severe Hair Loss?

the past few weeks i have started malting lots of hair its never normally like this it is just falling out all over its only thin strands but lots of them, why is this? also i am losing weight and not meaning too i had a baby 4months ago and i am now slimmer than was before i was even pregnant with him? please advise me on why this is happenin? (im only concerned about hair loss, i dont want to lose weight but its not a worry ) thanks.