I am currently planning to spend a few days in San Pedro, the go down to Tobacco Caye, then up to Cayo and over to Guatemala to see Tikal, Flores and Antingua. It seems like this is more of a two week trip though so I am looking for ideas of other places to see in Guatemala or I was thinking of going up to Chiapas for a little while, does anyone have any advice on itineraries?

Looking at the places you're planning on visiting, I'd suggest looking at a loop through Belize and Guatemala, and re-entering Belize from the south, rather than backtracking.

From Antigua, look at heading towards the Rio Dulce (try the lovely Hotelito Perdido on the Rio Lampara which has recently opened - http://www.hotelitoperdido.com">www....itoperdido.com), and then on to Puerto Barrios to catch the water taxi to PG in the Toledo District of Belize (3 crossings daily). From there you can spend some time exploring southern Belize and/or dive at the Sapodilla Cayes with ReefCI (http://www.ReefCI.com">www.ReefCI.com), and then head north up to Tobacco Caye.