I have noticed increasingly lately that my concentration, memory, both short and long, ability to think and concentrate and functioning is notably impaired. I seem to be in one place but another in mind, never really with it and often finding myself not really listening to people even going into a trance and finding it hard to snap out of going into myself. I have been under a lot of mental stress lately, loss of someone close, generalised anxiety, became a new mum, moving house i could go on. Could this just be severe stress or could i be going mad?

Yes, absolutely severe stress can cause many issues. This certainly includes your mental functioning. Difficulty concentrating, lack of focus, grief issues ("lost someone close"), new mother, moving. Your stress is very high at present.
Also generalized anxiety can be a separate issue or it could be connected with the stress you are experiencing. I do hope that you will consult your Dr or other health care provider to discuss these issues in depth. If you do have depression it is very amenable to treatment with the caution that treatment is more helpful the earlier you take yourself to your Dr. (many of the symptoms you mention are indicative of a depressive disorder). I wish you Blessings of Health, Julian of N