are bobtails subject to DOT rules?

Ive been driving for this company for 6 months and I drive a small bobtail and and bigger one (24 ft). Lots of times they have had me driving anywhere from 15 -22 hours straight. This past Tues I started my day at 6am I left Clear lake, tx then went to Tomball, tx then drove to Beaumint, tx then went to my last pick up in Boutte, Luisiana then waited for an hour for customer to show, then back to Clear lake, tx to drop off at 11:30 pm that night.all this was continous driving and they made me come back to work at 5am the very next day. .I know that people that drive the rigs are subject to a limit of hours of driving per day, but my question is " I have a Class A CDL but I'm driving bobtails right now, am I subject to a limit of hours driving ? Thanks for any help

 

A box truck or I guess its called a straight truck also.