Iphone 5 microphone is not working?!

My iphone 5 charger port was faulty then stopped working all together. By saving myself $80 I decided to do it by myself. It was a bit tricky but I eventually did it and everything was working perfectly fine.

Then a few weeks later my mic would start to play up by not working about 50% of the time with my phone calls. But Siri will still hear me 100% of the time. In phone calls, swapping to loud speaker will sometimes fix the problem but not always. What could be the matter? How can I fix this?