Why am I having issues with my sim card reader?

My phone had been working well for more than half a year. Suddenly, I started having trouble with my sim card reader. Most of the time, it says there's no signal detected/emergency calls only and can't send text messages, call or use my mobile data. There are times that I can receive calls and texts, but it's pretty unpredictable. Usually, I can fix the issue by restarting my phone, but it reverts back after a few minutes. I've dropped it a couple of times (at most just a meter high, never higher than that), and dropped it in shallow water once.