I have a small circuit with an ESP8266, a DS18B20 (here is the ds18b20 datesheet) temperature sensor and a DHT22. I prototyped everything on a breadboard, and it worked fine. I then moved to soldering everything. My input Vcc is 5v, so I am using it to power the DHT22 and the DS18B20, and the same 5V are also going to the LM1117. Problem is, the LM1117 outputs just 0.65V instead of 3.3V, which is too low to power the ESP8266. I also tried to unsolder everything and just leave the LM1117 alone, and it still outputs 0.65V. Moreover, I changed the LM1117 with another one to check whether it was a malfunction, but it didn't solved the problem.
Any idea on how can I investigate this issue? Where is it possible that I am losing so much voltage?
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You are not "losing voltage". The device is not turned on. The circuit of the chip shows a BE junction from the output to ground. If your ground pin is floating then you would expect to see what you see now - and of course the circuit would not be functional. Check your ground pin.