My "free" time - please don't take them away from me

The one thing that I find so irritating being a SAHM is that everyone assumes you don't work and will have plenty of time to run errands or do things for them. OK, most times I do help out when I can since I am the only "free" person around it seems, and that I can handle lugging my 3 boys around wherever I go. But sometimes, I can be a little too much for me to handle too.

It's true that since we moved back to my in laws place, I hardly have to do housework and this year with my boys all in morning sessions, I do have "free" time in the morning where I am free to do things. Well, since everyone knows I have these "free" time slots, I've been tasked to run errands, do this and that for them. I became the backup for everything...from housework to babysitting to returning library books to doing shopping to "checking things out" to chauffeuring etc, anything that you can think of that I can handle. I don't mind doing for my family but sometimes when they put it such that they are not asking me for a favour but throwing it to my face and telling me to do it, that gets on my nerves. Who are they to assume I have all the time in the world to serve them? The best thing is, they don't even bother to ask if I have the transport to do it...they just assume I can fly from point to point on my own.

How do I put it across to them that I am not their cheap labour but am doing a nice favour by helping them out but do not take me for granted. There are special persons that I will do anything for them, but the one asking may not be the special ones. I do need time to do my own stuff and even if I waste my time reading or blogging, it's simply my own time and free will to do. After nearly 9 years, I've finally found some peace and quiet time to call my own and spend it lavishingly in my own way and suddenly I find myself being more overwhelmed than before and spending time away from my own things and fulfilling others. So, please please do not take my precious time away nor take me for granted. If I have to harden my heart to say NO, I'll do it. I need my ME time, gym time, reading time, organizing time etc. I don't have to agree to everything I am "tasked" to do if it's not my concern.