From your description, complete picture does not emerge. Something that can be infered here is - your lack of assertiveness, and it is affected by our beliefs. People with low self-esteem usually lack assertiveness. Few steps that you can take are as follows- 1. Start voicing your opinion without hurting the rights of others; start with small things and then move to bigger ones 2. It is really important to learn to say NO 3. Don't keep feeling guilty for not doing the things the way others want, it does not make you bad; examine your belief structure 4. Many a time, we assume that people should understand our needs and feelings without we expressing them. It's not the right approach and make it a point to express your needs and feelings explicitly.
You will not be able to change this over night so make a plan to systematically work on this. If you continue taking small steps for some time, you'll see the change and enjoy it.
If you feel the need for further expert help, consult a psychologist.
Wish you good luck.