How can I get 3G back on my phone?

I have a Sony Ericsson Vivaz u5i which is a pretty old phone I got back in 2010. When I first got the mobile phone, I had 3G up the top of the phone but now theres a 'H' ? I'm not sure what it means but I really want my 3G back? What do I do to get it back? And what does H mean? Thanks heaps!