VPN constantly disconnecting and reconnecting - tried everything

I thought I had been using my VPN for months - turns out it was disconnected. So I turned it on and now cant work properly due to it constantly disconnecting and reconnecting. Several times an hour. My internet connection is fine. I am working from a signal booster as my office is too far from the modem, but I have no connection problems generally and this is the only way I can work in my office. I have no other firewalls on. There is no particular website pr activity which causes the issue. What can I try? I have tried everything Avast suggest. The VPN is the only reason I have Avast, but its pointless if i cant use it.