I was sad to read your post and of the loss of your husband. Five months is not long when you have lost someone you love and I think your description of of feeling as if you are climbing Everest is so true. Everything is such an effort and it is all too easy not to bother.
People can be very foolish and say unthinking things so it is not surprising you feel raw and sensitive. When I lost my Mum to cancer two years ago our next door neighbour told me Mum had had a good death and it was her time to go. I was literally gobsmacked that someone would be so tactless.
Feeling tired is something many people seem to experience. I still feel tired constantly two years on! I have resorted to having a little nap in the afternoon if I get home from work early which does help a bit.
I am sure your friends would understand if you said you didn’t feel up to going out at present. Being out and with what feels like crowds of people can be quite unnerving. If you tell your friends your concerns they might have some ideas for little meet ups, at each other’s houses for example. Nothing too pressurised and not a disaster if you only manage 30 minutes or so before having to go home.
Grieving is a long process. When you have loved someone so much of course you cannot carry on as if nothing has changed. Just keep taking each day as it comes. I am not going to say it gets better, it gets different. The pain lessens in some ways.
Mine is a niggle every day, knowing something is missing from my life. I take time every day to remember my Mum, think of the things we did together and the fun we had. I am grateful to have had both my parents company for so many years and that they gave me so many memories to think about.
Take care of yourself