'95 jimmy still leaking antifreeze on 1995 GMC Jimmy

I have the '95 jimmy leaking the coolant,I replaced the heater core, and it's ok. It's leak is coming down from on top of the oil pan somewhere, any ideas would help I'm stupped and having a little bad car luck. Thanks!

Asked by for the 1995 GMC Jimmy
Check your freeze ( expansion ) plugs on the back of the cylinder head and back of the engine block because they do fail. Napa # SEP 3818058

Better get an estimate from a repair shop, Expansion plugs can be tough to remove and replace
Thanks for the help!!! I am pretty sure it is the (expansion) plugs, but I can't seem to get to them. Is it an easy job, or should I take it to a shop?
2 more answers
Is the coolant toward the front of the engine or rear of the engine? Since you just replaced the heater core, make sure the heater hoses are sealed well. Are you sure this is not residual coolant that leaked when you previously disconnected the heater hoses and removed the heater core?
Sounds like if it's the front of the truck that its the water pump leaking. I know i just recently found out mine was, it took awhile to figure it out because i never seen it leaking on the ground