5 month old DS2 has started clawing at things. My boobs whilst he's feeding, my hands whilst he's sitting on me and other things such as his sleepyhead when he's in his cot (awake). He's clawed at his legs and left marks on them in the bath tonight 
Is this a normal part of development in that he's just discovering he can do this and testing it out, or is it an indication of something else? He seems pretty frustrated when he does it.
He's EBF and is on ranitidine for reflux. He's a grumpy sod and not a great sleeper but otherwise fine in himself.
Thanks in advance for any nuggets of wisdom.