There's a chance that your starter may have a microbial imbalance with too much bacteria to yeast. Starters that get super bubbly or frothy in the first few days and then fail to rise at all later are often struggling with this imbalance between naturally occurring bacteria and wild yeast. Discard your starter and begin again. For best practices, consider using an established heirloom starter which will ensure an appropriate balance of bacteria and yeast. Additionally, work with bread flour or all-purpose flour as problems are less likely to occur with these types of flour than whole-grain alternatives. Lastly, avoid starting your sourdough in hot weather as the heat of the kitchen may create an imbalance between bacteria and yeast, contributing to failed results.