My photos disappeared after reprogramming my iPhone 4
Since you don't have a backup, you will want to put the phone in airplane mode and stop using the device. Then see what companies do data recovery from iPhones. 

It is trickier than recovering data from a hard drive since SSD/flash storage allocates things differently than a sector based disk does. Also, the passcode and pairing procedure make mounting the raw storage harder. 

You should expect to pay some $$ for the service. The specific model of iOS and hardware will increase or decrease the cost as will your location in the world and if you need quick service vs sending it off to a lower cost location for the recovery work.