Clunking under the car

In the past couple of weeks I have had a few problems with my car. The last time I got an oil change I was told that the plug for the oil was the wrong size and that is what was causing me to lose oil and I had to get it changed. I had somebody change it and it was fine until a few weeks ago when I brought my car into my mechanic to get a new radiator. Ever since I got the work done on my car, there has been a lot of oil dripping onto my driveway. The weird thing is that when I check the oil, the dip stick says that I am good on oil. The other thing that has been going on, is that I can feel/hear a clunking sound coming from under the front end of my car. This usually occurs when I am stopped and then accelerate while I am driving. It also happens sometimes when I am making a turn. Do you know what could be causing this?