Engine sputtering?

I bought this car last night. It drove okay and then today on the way to work it kept sputtering. The sputtering seems to be getting more intense the more I drive it. It doesn't do it the whole time driving but seems to do it sometimes when I first take off and then go away and happen more around 40-60 MPH. Sometimes it doesn't really do it at all. I think the guy who sold it to me must have put Lucas stabilizer in it or something (he was also a mechanic) because it drove fine yesterday and it seems to be progressively getting worse. Also the engine had white smoke coming from under the hood once earlier today but only a short time. I don't know if it has a blown head gasket, it seems to drive fine when it's not sputtering. Even when I put it in reverse once today it started sputtering until I gave it more gas. Like I can give it more gas while driving to get out of it. But sometimes it just does it on and off while I'm staying at 60 MPH. I don't know if I should try to get rid of it already, if it's even going to last long because it seems very unpredictable, like it could be on it's last leg and then when it's not sputtering it seems fine. I really need a vehicle and spent all my money on this (only $1,500.00 and now I'm broke!). Any help would be greatly appreciated!