Is It Unhealthy To Loose 20lb In A Month?

I'm a 17 year old guy and 6'2 and I used to weigh 250lb, but it was a combination of muscle and fat. I'm the strongest guy in my high school and can bench press 230lb. However, I started feeling a little insecure so I started dieting and working out more and in 3 months I lost 10lb and was down to 240lb. I continued eating healthy(no junk or fat foods at all) and continued working out for the next 3 months but I didn't even loose 1 pound. So I was fed up, plus there is this girl I really like and I wanna look good for her so I really cut down on my eating, I skip a meal a day(a lot of the times I don't eat anything the entire day other than a apple) and working out to the extreme(not just weight lifting but also cardio) to the point where I can't even feel my body anymore and its not even been a month yet and I lost 20lb and dropped to 220lb and still dropping. I feel stronger then ever, but I also feel very light headed a lot of the time and my veins are starting to stick out of my neck and arms. So yeah, I was wondering if it's a little quick to loose 20lb in a little less then a month? Also if it is unhealthy, if I continued it for like 2 more months do you think the benefits will outweigh negatives?