Cadillac: 97 STS - overheating and oil light, blown head gaskets, low oil pressure

Question
1997 Cadillac STS
I think that I have two issues:
* my car has required that I add coolant every so often (once a week or so)  I recently had the AC repaired and now I can't drive more than 20 minutes in traffic before my car begins to heat up (190-210 has been the average for this car in the past).  When I travel at highway speeds, it's a bit longer.  There are no visible signs of leaks.  How can I tell if it's leaking internally and how do I fix that?  Is it pricey?
* My oil light blinks/flashes when idling in hot weather.  I checked the manual and it indicated that there is some sort of a flow problem.  Do you know what this could be from?  How can I fix that?

Thanks a ton for your help!
Joel  

Answer
You need to make sure that BOTH cooling fans are working and if they are, have it tested for blown head gaskets.

If the head gaskets are leaking it can dilute your engine oil with engine coolant and cause your oil light to flicker due to low oil pressure.