milk supply disappeared

I gave birth to my son a little over a week ago. My milk came in when I was 3 days pp. I started off getting about an ounce, then I’d get 2, and then 3.. the most I’ve gotten out of pumping is 4oz. My baby stopped latching to my nipple because we were bottle feeding him what I had pumped, this changed when I got nipple shields. I mostly nurse him now, and I haven’t been pumping as much. But my supply has gone down so much when I pump. I just pumped for the first time today (tonight) and I only got an ounce out of both breasts combined. I’m 18, healthy & I had previously been getting 4oz out of a pumping session. I’m just wondering where my milk went.. It’s really been getting to me because pumping a lot of milk made me feel really good about myself.. and now I just feel defeated. Should I be pumping more? Should I pump after I nurse him? Before I nurse him? Pleaseee let me know!!