In an ideal world, the lengths of the elements on your TV aerial should be precisely measured to 'resonate' perfectly with the incoming frequency. However Freeview channels are transmitted in 'bundles' (called 'multiplexes') with each multiplex using a different frequency. As there are 9 main multiplexes (combining together to provide coverage of all the principal Freeview channels) you theoretically need 9 different TV aerials on the roof of your house.
That's clearly not practical, so we actually use aerials which are only a 'rough match' to each of the different frequencies that they're required to receive. To make things worse though, unless you've had a new aerial installed since the digital changeover, the aerial on your roof was never designed to resonate with
any[i of the Freeview frequencies. (Analogue TV was transmitted in an entirely different frequency range). So it's unsurprising if it struggles to do its job properly.
When the digital changeover occurred it was predicted that around a third of all households would need a new aerial. It turned out that far fewer actually did but it should be no surprise that what most people have now got on the roofs of their houses are actually little better at receiving Freeview transmissions than a bent coat hanger might be.
Channels 107 and 113 (among others) are transmitted by the 'COM 7' multiplex, which has now moved frequency in some areas. (That's occurred as part of a Europe-wide telecommunications agreement, designed to free up part of the radio spectrum for use by mobile phone services, etc). Your aerial resonated fairly well with the old frequency but, it seems, very poorly with the new one.
You [i]might] need a new TV aerial but, in your situation, most people get away with simply installing a signal booster, such as this one:
http://www.argos.co.uk/product/5713543
(You'll also need a fly lead to go with it:
https://www.screwfix.com/p/fly-lead-coaxial-plug-to-plug-1m/41720 )
Once you've installed a signal booster, carry out a further retune of your devices. (NB: If you're offered a choice between 'adding' channels or 'replacing' them, ensure that you select 'replace'. It's important that you force the device to wipe all existing channel information and to then go through the set-up process as if it was a first-time installation).