Weight Gain Insecurity

My little boy is very long but so so skinny. Every time he's weighed he's dropped further down the centiles for weight but remains 90th for length. No medical professional is concerned yet but as I'm EBF it's making be feel so insecure that my body isn't giving him what he needs. I'm an over supplier so it's not a quantity issue but my milk just doesn't seem fatty at all 😔 does anyone else feel this way as it's making me so blue?!