having to supplement

I recently got pregnant and I noticed an immediate drop in my supply. Just took my 8 month old to the doctor and they told me I need to start supplementing. I know it's not the worst thing in the world but I'm so upset I cried the whole way home partially because I feel like I was starving her this month and partially because I really wanted to keep exclusively breastfeeding. I'm just so upset I'm hoping I can get my supply back up I got lactation cookies and I'm gonna make it a point to drink more water. Hopefully it's not a lost cause at this point :(