Is my supply reducing

I exclusively breast fed my baby till he was 6 months. He is almost making 7 months so I feed him with solids once and breast feed the rest of the time. He drinks. But I nolonger feel like my breasts get full or hardly do I ever feel any let downs. Due to this, I stopped pumping. I used to pump between feeds when I felt like my breasts were full. Baby is still drinking from me fine but I want to do STH to increase my milk supply again. Because I only have about 20 bags of frozen milk. I wanted to store up enough for him to drink when I wean him off the breast. Because I want him to have milk until he is 2 years.

Or is this normal for milk supply to get lower as baby grows up?