Hi Tomato,
family business -> u might want to change ur job again if there's no opportunity within.
There can be many different reason why ur manager treat you this way...
Let me raise one common mistake I see and you see if it fits ok? Cause hard to pin point the root cause with the limited information..
Often, new people neither appreciate the fact that others have spend a lot of thoughts and effort into things like workflow/business process design. Nor did they understood (or at least perceived by the manager not to have understood the topic to a good level) before they start giving suggestion or become critical.
If you are already an experienced person and understood the company, plus your boss have already witness and acknowledged your capability, you would more likely to be successful when you are raising suggestions in a straight forward approach.
If you are new, it would be better to approach any suggestion/question you might have using a discussion/collaborative approach. Before you raise a suggestion, ask your manager why is it design this way. How did it solve the issue or how does it support the operation. After you "show" your boss you have seek and understood his design, then you raise your suggestion. If you wanna raise to him any problem with the design, first seek to understand his design, then ask critical question on how his design is going to cater to a problem which u anticipate would occur. If he can't answer you. Then you give your suggestion.
If you are new, people would always doubt whether you have understood or study the topic enough to suggest. And yes, most likely your suggestion would be wrong since you did not do as much ground work. If you do it without seeking to understand the topic deeply first and is wrong in your suggestion, people would see you in a bad light. It also reveal ur poor communication skill and ability to collaborate with others.
Even if you are right, you are putting urself in a direct confrontational situation, telling ur manager that I'm just here and I'm right while u r wrong. He/she loses face. Who want to lose face to a newbie?
Go with a discussion and collaboration approach. It'll be much better received.
As for your PM, many PM have vast experience and have a tough character. But they have plenty to share. If they correct you. You might be better to listen and try to learn from them. There is a lot of reason why PM do certain things in a certain way, which are not understood by others. But those things helps to attain project success, even if others don't understand it. Go one step better. Tell them that you like to move to PM role one day and ask them to teach/mentor you with each comming project =) Most would be v glad to do so. Even if u don't pick up anything, u'll gain a deeper understanding of your PM's expectation and style, which would help.