1. Please check if you have properly configured your APN settings. your APN must be configured to http.globe.com,ph for prepaid.
2. The signal you are receiving might be congested. if your phone has 4G or LTE capability or vice versa to 3G or HSPA+ mode, try to switch it to that network mode. Signal strength is not a guarantee that you can browse the internet specially if you are in a heavily populated area.
3. Try to restart your phone, close all other apps that consumed heavy data bandwidth.
if you have done all these things, try to assess your phone if this has enough capacity or RAM to handle your browsing needs.
Hope these helps.