employment issues.?

Work for a small community hosp. Hours are PRN. Recently was changed to 7 days straight 8 hr shifts. Asked if this would be clasified as FT. Was told no we only have 3 FT positions. But there are 4 shifts. I come in when ever there is an opening. Do not go home early. And have never said No I can not come in. Even with less then 30 min notice that I am needed. Well today I said no. I am suppose to be at work tomorrow A.M. (5 o'clock) But they wanted me to work till 11 this evening and then come back. Is it wrong to feel a little under appreciated from this company? And should I start sending out resumes? Is this turning into a dead end job?