Stress and diet

So I'm 6 months pregnant and I've had a rough pregnancy so far. Last time I got bloodwork done all was good but I'm due for more testing. I'm just kinda stressed because I have trouble maintaining a balanced daily diet. I have a normal bmi but I'm not gaining as much as I should. Some days I just feel sick or don't have a big appetite. Other days I eat really well, it just varies. I feel bad when I don't eat well enough because I know it's important for baby. Anyone else struggling with this, or have any tips?