2000 Nissan Maxima overheating

In the last month or so, I've been hearing a weird whistling sound coming from my engine when I start it. Okay, fine, it's an old car, so I didn't think anything was really wrong.

Fast forward to yesterday, (7/7/16) and as I'm leaving work the temperature gauge starts to move toward H. I was so confused. I turned of the A/C; still overheating. Came to a stop, drove fast, drove slowly, and no matter what I do, it overheats!

Tonight on the way home, it actually went past the H, and I got nervous; I had to make a stop anyway, so I pulled over. It sat for 40 minutes until I came back out of the store; so I thought, well, maybe it's had some time to cool off. NOPE. Within 5 minutes of driving, it start overheat again. Now my engine has this sound like it's running hard, and a bit louder than it was before. When it happened yesterday, there was no steam, but tonight was pouring rain, so I couldn't tell.

I called my mechanic yesterday from the road, and he said it may be the fan or the relay. But I can't get to him until my day off, which is Thursday of next week. I'm starting to think I won't be able to continue driving it until then!