Hi,
Our betta recently had constipation but is now fully recovered. Feeding more bryne shrimp will only clog up the digestive system further as it is a very rich food and should only be fed once per week. If your betta will not eat the pea (ours refused too) then daphnia should work (it did for us), you can buy in the LFS in frozen packs in cubes or sometimes live in small plastic bags marked as water fleas. If you do get them live then drain the water out first as it is likely to be in pretty poor quality and will only reduce the quality of your aquarium water.
Just feed a small amount of daphina (less than a quarter of a cube every 48 hours) and after 2-4 days it should gradually clear up. A week without food seems quite a long period of time to me so if possible try and get the daphnia today and feed a small amount asap.
Hope that this helps.
Ed