The 'kit lens' that you have (18-55mm) is very often of not great optical quality, having been made for a budget price to 'bundle' with the camera. On the other hand, it's a very useful size for most of your shots.
Next problem.... it's probably a little 'slow' - by which I mean it's maybe f3.5 or f4..... you really want around the f1.7 to f2.8 max apertures to get really sharp - and give faster shutter speeds. You may say you take everything on a tripod but those bigger max apertures will put the backgrounds into a nice soft focus or completely blurred, giving a good 'bokeh'.
You don't mention lighting (apart from the reflector)..... you may like to investigate the use of 'continuous' lighting (aka 'hotlamps' but in fact not hot nowadays)..... reasonably powerful lamps (at daylight temperature) but cheap. A pair won't cost that much.
Your reflector is probably very useful, but you can build (masking tape) white thick card (or "foamboard") to make much larger reflectors - then bounce your lighting (even daylight) around well - and softening the contrast. Do the same with black thick card and you can reduce reflections around the subject.
More backdrops ..... and you could build a decent backdrop stand out of long poles (strong dowel) and some cheap brackets..... like football goalposts.
The subject of studio lighting is huge, so check out some lighting sites..... e.g.
StudioLighting.net
for tutorials, or even YouTube.