Emily it's ok i have the same problem, the best thing you can do is feeling your breathing and your heart beat, if you can't do both just your breathing. What i do is just be that's it. Now i've altered states of consciousness but nothing major yet or getting any answers to my life's problems. I must go deeper and relax more
Also Relaxing is very helpful you don't want to try so hard
For Christmas my sister got me one of those giant sit up pillows for reading books, and i use that for my back, and it's like wow that makes a different since i have a hard time keeping my back straight for meditating.