If you don't already have it get yourself a copy of The Nursing Mother's Companion, it's a great book for nursing moms.
I had that problem with my oldest. The change probably has something to do with teething or separation anxiety. Or a little of both. The eating less during the day might be because of teething and the nursing at night may have to do with being hungry because of eating less during the day. I found the pain scared her and caused her to want me, thus the separation anxiety. It's totally normal for a baby to go from sleeping through the night and then start waking up once or more a night it happens when they learn to walk and again at about age 2 (so far I've found that continues periodically until at least age 8).
I found that separation anxiety usually came before some milestone of independence. Once they achieved the new independence whatever it was they were fine. I have to say I gave up & took my girls to be with me while these spells passed, I couldn't stay awake and neither of mine ever cried themselves to sleep effectively, they could both go all night.
There is a way to cut down the duration of separation anxiety that I have found very effective. Litterally be in their face constantly, hugging, kissing, holding, carrying and generally not letting them go until they're totally sick of you and want to get away (you let go a little after they're really sick of you) for some reason they feel like they've gotten enough and stop with the clingyness within a few days, sometimes hours. That continues to work with 8 year olds as well, in fact that works a lot better when they're older, now my daughters can only tolerate maybe 1 to 5 minutes of being 'loved up' then they're done with me.