Emma, it sounds like you are having a hard time I recommend you call the ABA 24 hour toll-free helpline on 1800 mum 2 mum (1800 686 2 686, drop the last 6 for VOIP). They can talk to you about increasing your supply again (feeding frequently is the number one thing), and also have a fantastic booklet about breastfeeding and PND which costs just $5. Even if you do need medications, there are many PND medications that are safe while breastfeeding. THe link marcellus posted is very helpful also.

Take care hun.