NBR: So frustrated right now, aka vent

I suppose I shouldn't complain because it's my first write up ever, but my assistant manager pulled me aside to give me a write up today for being late to work, one time, almost 2 weeks ago.  She said our manager asked her to give it to me and had already spoken to me about it, which is not true.  Secondly, in hindsight, I realize that 7:30 am is a perfectly reasonable time to expect traffic on the road and I should have anticipated that, but I am used to working either late in the evening when there is no traffic going to work, or super early in the morning (3:30 am) when there is also no traffic, and I just recently opened up my availability, so I really just didn't think about traffic even being a problem.  I made an honest mistake.  I don't think I should be penalized for it.  Luckily my assistant manager was supportive and agreed with my decision to talk to the manager before signing the paper. 

My frustration is with the manager, who is new to our store as of 2 months ago.  She has come in, changed everything we were used to, makes promises she doesn't keep and then expects us to be perfect or else.  She knows I am pregnant, I've talked to her multiple times about scheduling me shorter shifts because of the severe back, hip and foot pain I've been getting from standing the whole time, and she'll give me 4 to 6 hour shifts for a week and then it's right back to 7 1/2 to 8 hour days again the next.  I've never worked such a physically demanding job for such s#!t pay in my life and I feel so stuck. I feel like I barely help my husband with the bills we have now with the little I make and yet we would be in big trouble if I had no job at all.  If I weren't pregnant in need of benefits and doing field work for my Master's during the day (needing flexibility to work this job at night) I'd give the "Eff you, I'm out!" speech in a heartbeat.  Maternity leave will definitely be spent looking for something else.

If you made it this far, thanks for letting me vent.