Problems with a 1998 Toyota Corolla

I have a 1998 Toyota Corolla with over 160,000 miles(it is a standard, not automatic). It rarely gives me any problems but suddenly two days ago it starts to run rough (as if it is not getting a connection or something, "putt, putt" sound). This morning I had my inspection done and the guy seemed to think I needed to have my clutch replaced (the car passed inspection, then suddenly after leaving I noticed this sound became quite frequent and a pinging sound accompanied it (along with the check engine light flashing). I became very conscerned at this point, especially because these signs came on very suddenly. When I voiced my concern to my non-mechanic husband he took a look at the oil and said it did not register. He then put oil in it and let it sit for a while. I took it around the block later to see if there was any change, but there was not. When I went to drive up into the driveway I noticed what looked like a very large oil spot. Now I am really really concerned that it could be something major. I do not have a regular mechanic and am very concerned about a costly repair, being that we are very very tight on money right now and are bearly getting by. Please give me any advise you can. It would be greatly appreciated. Thank you so much.

~Misty