I spent a good deal of my pregnancy in tears, (mind you, I was in a miserable relationship!) but my advice would be to let yourself have a good old cry if you need to, but then decide when it's time to stop. Visualise a red stop sign, and change what you are doing- go for a walk, watch a movie, bake a cake, whatever! It's ok to cry, but you need to set some boundaries for when it's time to stop feeling miserable, and do whatever makes you feel beter. Concentrate on keeping healthy- it's good for your baby and makes your after- birth recovery much easier if you exercise lightly and eat well.
This is what worked for me- hope you're feeling better soon!
As soon as you have a baby to care for, you'll have all the more reason to treat yourself better!
Ellie, NSW, DD 3 yrs & TTC # 2