You'll have to be a bit more specific.
What sort of speeds are you getting using something like SpeedTest?
What were you getting before?
Are your APN settings configured correctly?
Text "APN" to 50048 and follow the instructions to make sure that they are:
Where are you located?
Do you know any other 48 users in the vicinity to check with them how they find things?
If you need to contact 48 support about this then see the links in my signature below.
