I believe echinecea is safe.
however, it's not going to help once you're sick. you should only take echinecea during cold season or if you've been exposed or if you're starting to feel a little down for a short period of time, less than a week, I believe. Once you're full on sick, the cow is out of the barn, so to speak, and it's not longer effective. It shouldn't be taken long term. There's another herb my ND said was in the same boat, but it's a lot stronger, and she's noticed that they've been adding it to remedies for illness, but it's a preventative and too harsh for taking long term, I think it was Acerola? I could check.
Anyway, the thing to take once you're sick is golden seal as it is a natural antibiotic, however, I don't know if it's safe during breastfeeding. It is definately contraindicated in pregnancy. You can take garlic, it's antibiotic and anti-oxidant.
I don't know what else to suggest, sorry. Sorry you're feeling down. Hope you feel better soon.