Coolant not returning to radiator and now will not start

Vehicle listed above has been showing signs of a blown head gasket; low power, fluctuating temperature gauge, heat working sometimes and not others, air in the coolant system. After a while the coolant will build up in the reservoir and not be sucked back into the radiator. There is also a gurgling and whirring sound behind the passenger's side dash which I hear when I shut the car off.
I have emptied the coolant out and refilled the coolant into the radiator twice which has fixed the temperature fluctuations and heat issues for a short time, but it just happens again eventually. I used a head gasket seal detector to check the coolant and it showed that it was, definitively. I ended up putting k-seal head gasket repair in which didn't help at all.
Now, today, I went to start my car and it wouldn't start. I eventually put the accelerator to the floor and turned the key which got it started but this had never happened before. There was a strong gas odor under the hood when I tried the first couple times (before I floored the accelerator).
Are these issues all a symptom of something in particular or is it a lot of different issues? If it is all because of a blown head gasket, why didn't the k-seal fix it, and do you have any advice on what to do (besides obviously bringing it to a mechanic for at least a grand or trying to fix myself which is a little too much for me)?