Milks slowing down :(

Ashley • 20 years old♍️ One daughter born on October 31st 🎃 In love ❤️
The past couple of days I noticed my milk supply going down a bit. When I pump, I only get 5 ounces. 
Tonight really showed how bad it was getting. 
My daughter was acting SO upset and crying and I kept giving her the breast because she was acting like she was hungry. But she didn't seem satisfied and that was really odd to me. She also wasn't making the "drinking noises" she always makes. I did her bedtime routine and she was so upset until I gave her a bottle of breastmilk and she aggressively ate it and fell right to sleep. 
I feel like I'm failing. I returned to work last week and started me off with 7 hour days and I have 5 hour days this week. I can't pump at work. There's literally no where to do it and I don't have a manual pump. 
I want to cry. I love breastfeeding and I've had it so easy with her. We've never had problems with it. I don't have anything against people who use formula but I just don't want to use it with her not pay the ridiculous price. I don't want it to come to that.  
I'm just feeling like a failure. That she was so hungry and I didn't realize my mistake sooner. :(