help! sudden engorgement

Brianna
So I've been bf for almost 5 months now exclusively. I pump occasionally to build up a supply but not much. Yesterday, I fed my baby like normal (right now she eats every 3-4 hours during the day. Goes sometimes longer at night). I missed one feeding last night,  my husband gave her a bottle of bm. (I've missed a feeding before without pumping and I will get full but never engorged) Then I fed her right before bed around 8. She woke up around midnight when I fed her again (both sides). Then, I woke up at 3am with my left side so huge and rock hard. It was leaking like crazy and so engorged. My right side tho felt completely normal. It was so bad I had to get up and pump just my left side. I pumped about 6 oz on just that side and I couldve kept going but I stopped because I knew I was
Going to have to feed my baby again soon. So it still felt fuller on the left when I was done. Well she woke up after that, I fed her again on both sides. Now, 4 hours later I wake up and the left side is huge again. Not engorged just yet but fuller than it would usually be. 
I looked it up and I only read things about a clogged duct but there is no pain, I'm definitely having a let down on that side. Milk is flowing. It doesn't feel extra tender or sore or anything. Anyone have any ideas?