Hi K., you already know that giving in doesn't help the situation. This is because when your son cries to get what he wants, he knows that he can just cry harder and you eventually give in. He remembers that crying harder worked last time, so he'll try it again. He is not doing this because it's a mom thing, he's doing this because this is a pattern that the two of you have created. But, the good news is that you have the ability to turn this around before it's too late. You have to remember that you are the mom and you are the boss. What you say goes and you can do it respectfully.
Make sure your yes means yes and your no means no. If you give in sometimes and don't others, this creates a lot of unpredictability for your son and can contribute to his misbehavior.
Children need need limits and they feel more secure when a parental authority has some control over their overwhelming world. Everything is so new to them and they need someone to guide them and tell them what is ok and what is not. This helps them feel safe and secure (this may not be evident in the moment, but this is created by having consistent limits over time).
To start having some control, a great way to handle situations where you feel you may give in is to make up your mind about what is acceptable to you (i.e., no candy at the store) and tell him your expectations ahead of time so he knows what to expect. If he is upset, validate his feelings--"I know that you're upset right now. You really seem angry" (or sad, mad, whatever he is at the time). Briefly give an alternate option (i.e., we can't buy candy at the store right now but you can have a snack when we get home). It may not be what he wants, but those are the rules. Or, give him an option--ie., "you can either pick up your toys by yourself or we can pick them up together" (either way he's picking up the toys and it doesn't really matter if you help or not). Make sure you are ok with either option before you give them to him. Be firm when you talk, but not angry. Make sure your tone of voice is loving, but in a way that he knows you are serious.
Kids this age are really at a point where they want to implement some of their own independence. They have really strong feelings about this. Giving him two acceptable options is a way that he can have some control over his world but in a limited way. See the difference between giving him complete control where he is overwhelmed, and gently guiding the amount of control he has so that he knows how to make good decisions? This also helps him gain self confidence as well.
I work with toddlers and this is a common problem parents have with this age. The key here is to be loving and firm, validate his feelings, give him acceptable options, and be consistent. Let me know if you'd like to talk more about this. Sorry this is so long, but this is something I feel strongly about because I have seen the positive results when limits are set--it will create an even better relationship between you and your son! Best wishes, C.