OUCH...nipple pain but only in left breast?

cutestpi

I have been experiencing extreeeemly sharp pain in only my left breast while nursing. It feels like the typical thrush symptoms- like a needle is being drawn out through my nipple- but then begins to subside after about 10 seconds. No pain whatsoever in my right side. My baby isn't showing any signs of thrush. Could it just be from a shallower latch? (sometimes I do have to remind him how to latch properly, especially if i've bottle fed him the session before)... infection? or typical sore nipples that will gradually get better over time, he is 4 weeks old. What can I do to alleviate this, its really really painful and I have to phych myself up before he attaches and I'm usually cursing under my breath for a good 15 seconds.