Your eating bread will not cause constipation to the baby. However eating a lot of bread especially white bread can cause constipation in you. Limit to two slices a day and choose whole wheat or multi grain option. Frequent Stimulation is the best way to increase milk supply. There are some foods which work as galactagogues but bread is not one of them.

Eating bread will not make baby constipated. The articles given on the app are very useful

Also do refer to article section for articles on food for breastfeeding moms

Keep feeding on demand and that only increase or maitain milk supply.