If it's not a dvt what else do you think it might be? Any new medications etc?
If you've got a swelling/tenderness in one calf only then without a very clear alternative obvious cause you're likely going to end up needing a dvt ruleout first. i.e GP might agree possible gravitational oedema, but lets exclude the dvt first by being reviewed in A&E.
In my area the dvt clinic is in A&E, but only runs from 9-5, outside of that they will ask you to return the next day if clinically well, they may start anticoagulants before it's been properly diagnosed depending on how you present/whether you have any risk factors - (recent surgery, long distance travel, hormonal contraceptive/replacement, chemotherapy, bedridden>3days, previous dvt).
If you measure the calf at the widest point on each leg and there's around 3cm or greater difference this is also quite concerning.
If it is a dvt the risk is that a bit breaks off and travels to your lungs/heart/brain causing either a PE/heart attack/stroke.
The safest advice, and certainly what you'd get if you called 111, is to attend A&E for a face to face assessment now. Ultimately you've left in a while now already, if you went to A&E in the morning they would be better than not going at all. Either way, if you develop any sudden changes like a persisting chest pain, shortness of breath don't ignore those - either make your own way to A&E if anyone can take you straight away or 999.