Hi N., my name is J. (27 years old) and I have a 2 year old daughter. I also have years of early childhood experience in daycare, etc. Ist of all is he teething? Never underestimate the power of a teething child! Also he is definately in a transition time of baby becoming a toddler- it is normal. Also, Over the years I have seen alot of different children react to their new world in many ways. At around that age they are more aware of the fact that they can use their own body to get where they want to go without completely relying on you, yet at times they are afraid of not having you right there. They don't do things to defy you, rather they do things because this world is big place and they are still new to it. "testing the limits" also serves to expand their brain and conception of the world around them. They do however lack the ability to know what is safe or not and do not understand resoning, not to mention they have no way of communicating in the full english language with you, so they cry and lash out. My daughter was the same way. Basically I have learned that the best thing I could do was literally remove her from situations, distracting her with something right after. If she screamed, I just had to keep my cool til she got through it.
There are also different temprements of children/people. What I have observed is that different personality types will respond different. For example, since my daughter came out the womb, she has been active, curious, a "talker" and interactive with her environment.. Now there are other children who are more introvert and like to observe rather than participate, will cry or go inward rather than scream or cry, and are the babies who sit in the grocery cart the whole time the mother is shopping without a peep.
So basically, I think it is more important to observe what kind of personality your child posseses, now and in the years to come, and then try to realize why he is frustrated or clingy, etc. That has helped me tremendously with my daughter. She is not hyperactive or a terrror by any means, but she is and has always been very independent with a quick mind and an attitude like she can do everything by herself. And she's only now 2! But I love that about her and in time you will see that your son posseses a quick mind and you will love his enthusiasm for the world around him. All the while I think the most challenging thing about parenting is how to keep our cool when their fuse is sooo short and not to 'lose it' when they do. Taking a step out side, a stoller walk or putting music on are also ways I get my daughter ( and me) redirected out of tense situations. Just keep breathing, hope I was of some help! keep in touch if you want, J.