This is normal. The initial views after publishing a hub is mainly from your hubpages' followers. After this there is a drop till your hub is indexed in search engines.
Depending on how well you have included and used your keywords and tags the rise can be slow or fast.
Still for a hub to really get a footing on the search engines it takes about 4-6 months. Hence older hubs do better since they also get back links whether on their own or by use of social networking sites, forums etc.
You can help the HubPages community highlight top quality content by ranking this answer up or down.