Is it PPD or just stress?

My little guy is 8.5mo and ever since he was born I just am exhausted and not interested in doing anything. I have a history of dysthymia that I never needed medication for, mostly after my mother's death when I was younger. My little guy was colicky and cried all.the.time for the first 4 months, but is now happy during the day. He has reflux and a milk/soy protein allergy and I have my own food allergies, which both severely restrict my diet. He's still up every 2-3 hours at night to nurse. I work 70-80 hours per week, with wildly variable shifts. 

I still take care of LO and get out of bed in the morning. But I have no energy or desire to maintain the house, where I was previously a neat freak. Or bills are sometimes late because I just don't feel like sorting the mail, whereas before I was 2 weeks ahead. I never go out with friends, because if we mess with LO's routine, there's hell to pay. And I'm too tired to go out too. I have about 3 hours a day that I'm awake and coherent at home, and it's spent running to the grocery store, doing laundry or just spacing out looking at everything that needs done while trying to spend SOME time with my kid. My birthday is this week, and I don't even want to celebrate because I don't want to leave the house and I can't eat anything if we go out anyway. We live in a city with no family, and all my friends are coworkers with similar work schedules. DH works from home and takes care of LO.

I don't know if this is PPD or if I'm just so effing exhausted. No amount of meds will change my work situation or the fact that my baby is high maintenance. And I can't even go for counseling due to my work schedule. So I've felt like it's pointless to seek any help. Any advice?