2 weeks after getting bridges, it came off. It was recemented but loosened since. What can I do? (photo)

Images of the bridge which you have posted doesn't look very clear. It's very difficult to comment on. As the gap between the natural tooth and implant bridge looks a lot. I will suggest you to visit a prosthodontist - specialist for the crown / bridge and occlusion/ bite. The doctor will be able to understand what's the problem with the bite of implant. 
1. Many at times there is a lot of forces which are acting on the implant crown those needs to be assessed
2. If the bridge is a cemented one and space with the lower jaw is less for the bridge. You can ask your dentist to switch it to a screw retained bridges- these are fixed with implants using screws directly no cement in between- specially meant for situations where repeated dislodgement of implant crowns are there either due to less height of implant abutment or heavy bite forces. 
3. If heavy forces/ clenching / grinding is the reason behind repeated dislodgement, ask your dentist to make a protective night guard. Which you can wear at night or during rest ours to protect your bridge from heavy forces. 
Hope that information helps, Good luck!!!

Something is wrong here. If your dentist cannot offer a sensible explanation and assurance that this will not happen again, then get a second opinion. I do not understand why this is happening. Did you get a rock bottom price on your care?