1990 Isuzu Trooper overheating and smoking

I have the same problem! When it first started, I was told I probably had an oil leak or a blown head gasket. Knowing the cost of a head gasket repair, I was beside myself. Someone told me about Bar's Head Gasket repair, and I spent $30 on a bottle and it magically seemed to fix it - for a month. Recently, it started overheating regularly. I started carrying water to fill the radiator with then this occurred, but the radiator didn't seem to take much water, and the problem got worse. Talked to more people, was told water pump. Then was told no, thermostat, as no water is leaking, so its not water pump, its thermostat because current one isn't opening to get fluid to engine to cool it. I fixed it, and thought $15 bucks to save my only vehicle - cool! Cranked the engine, the friend who helped me said "hear that" that's your thermostat opening". I thought all was good. Took it for a test ride after letting it idle in the drive for about 10 minutes, and watched the temperature climb. And got it back home (maybe 4 mile drive) just in time to see it smoking. Thought maybe head gasket - orig problem, and went and bought another stop leak problem, I think this was called K Tech and was recommended by the guy at Napa. Put it in, still same problem, overheating, and smoke coming out of exhaust and from underneath. As you can tell, I'm no mechanic, but in looking at diagrams, it appears the smoke under the car is coming from in/around the transmission fluid pan, and the smoke coming out of the exhaus is while, vaies in amount, and is misty with condensation.
Please, this is my only vehicle, and today, in 100 degree weather, I had to walk in dress clothes to train (3/4 mile) take 2 trains, then walk the remaining half mile to work from there. About a 2 mile journey for my 21 mile commute. I am a single woman, and work in South Philly - I've felt more comfortable!

If anyone has any ideas, please throw 'em at me! I'm becoming handy out of necessity - I need this car and was unemployed for 15 months prior to getting this job a few months ago. I'll try anoything myself, as I cannot afford to go to a mechanic for either diagnostics or repairs.

I thank all in advance for yur help!