Other factors could be sleep and recovery. Don't tax your body too much with exercise- cardio and stress will increase cortisol over what it should be and wreck havok,, so get lots of sleep every night and if your body feels beat up, take a day of the cardio.
Danny- if you're exercising 5-6 days/week and lifting weights, you're likely also building muscle. When I was working out with a personal trainer before, I'd do cardio 5 days per week and lift weights 2 times a week... I ended up putting on weight, but it was muscle weight as I was down in overall percent body fat and inches.
I also agree with the previous poster... make sure you've recalculated your caloric deficit to reflect your current weight. If you haven't done that, you're likely still eating the calories you should from when you weighed more, and would likely be in 'maintenance' mode as opposed to 'losing' mode.
Your BMR is 1,725. At 2,000 / 2,100 calories a day you should be losing weight after exercise. Your deficit calculation seems OK too. So don't be in any rush to reduce your calories intake. At 18 you do NOT want to eat less. BMR is minimum for an adult trying to lose weight at 18 you should add at 250 to 500.
Hitting a plateau after the initial weight loss is perfectly normal. There are a dozen post on this forum by people to whom this has happened. Continue as you are. Weight loss will start again. Look for and read the other post about this issue there are some good recomendation to break a plateau.
The side effects of allergy medications keep some people from using them. Natural remedies can be a great alternative, but some are more effective than others.