Its normal for VM but no it should not drop that low.. place bets on it being "high utilisation" which means they have over sold the network your on, they will supply you with a repair date they have no intention of sticking to, thats if they even consider your 3Mb evening speed bad enough to even bother raising to the "network team" in the first place, either way your in for a LONG wait.
Virgin media, the UK's fastest broadband.... Why they banned that advert ill never know.
Sorry to read that you are experiencing slow broadband speeds.
From checking your connection, the upstream power levels are high and the downstream is too low at - 9 dBmV. As this can have an impact on your broadband, I would like to book an engineer appointment to check this over for you. I've sent you a PM (purple envelope icon, right corner) with some details for you to confirm.
I did also notice a high peak time traffic fault in your area which is causing slow speeds. Our networks team are investigating the problem and are improving bandwidth and performance to help with this issue. The reference number is F003661607 and with a review date of 28th December.