Loestrin 24 Fe and kno

I am 2 weeks and 3 days into taking this pill for the first month and I don't know if I should stay on it. I just started to get brownish blood/spotting and cramps in my back. I am afraid I might be pregnant although my boyfriend always pulls out on time. There is a chance that some precum got inside me, but I haven't been too worried since I don't think it's very likely to get pregnant from precum while on the pill. Should I be worried or are these symptoms normal? I also have had more frequent mood swings and anxiety, but I suffer from both anyway. From all the bad things I have heard, I am eager to switch back to Ortho-Tri Cyclen. Is there a big difference between the pills and the amount of protection they offer from getting pregnant? If any information can be given, I would really appreciate it.