Would love to help but can't as I have the same problem!!
Hot showers and hot herbal teas help a bit. Apparently nasal sprays work for some, but they make my nose bleed.
Just so you know, for mild antihistamines like Claritin/Loratadine, they actually are safe for your baby, but they can cause supply dips. I did used to take just one occasionally when my allergies got really bad, because I had oversupply with my son, so it wasn't a problem. My supply is a bit on the low side this time though, so can't risk it.
It's awful though, isn't it?! I really sympathise.